CN102323503B - Method for detecting inrush current distortion of transformer based on Rogowski coil - Google Patents

Method for detecting inrush current distortion of transformer based on Rogowski coil Download PDF

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CN102323503B
CN102323503B CN 201110224368 CN201110224368A CN102323503B CN 102323503 B CN102323503 B CN 102323503B CN 201110224368 CN201110224368 CN 201110224368 CN 201110224368 A CN201110224368 A CN 201110224368A CN 102323503 B CN102323503 B CN 102323503B
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distortion
transformer
current
degree
luo
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CN102323503A (en
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叶曙光
郭泉
贺枫
张志刚
李春
王宇森
常新平
汪斌
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JIANGSU LINYANG MICROGRID TECHNOLOGY CO., LTD.
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JIANGSU JINSIYUAN ELECTRIC TECHNOLOGY Co Ltd
JIANGSU JINSIYUAN ELECTRIC CO Ltd
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Abstract

The invention relates to a method for detecting inrush current distortion of a transformer based on a Rogowski coil, which belongs to the technical field of relay protection of electric power systems. The method comprises the following steps of: measuring primary side current of the transformer to acquire a differential voltage analog signal; acquiring a corresponding differential voltage digital signal; judging whether abnormal current occurs or not; performing cosine window-added Fourier transform on the differential voltage digital signal to solve effective values of every-time harmonic waves; calculating the degree of distortion, namely judging whether inrush current occurs or not according to the degree of distortion, and the like. By the method, the conditions that incorrect tripping of differential protection during on-load switch-on of the transformer is prevented and exciting current and fault current are strictly distinguished are ensured, a criterion value has extremely high redundancy, and the degree of distortion is accurately and reliably determined.

Description

Inrush current of transformer Distortion Detect method based on Luo-coil
Technical field
The present invention relates to a kind of method of differentiating the transformer exception reason, especially a kind of inrush current of transformer Distortion Detect method based on Luo-coil belongs to the Relay Protection Technology in Power System field.
Background technology
Luo-coil be a kind of employing with wire equably on the uniform nonmagnetic substance framework in cross section, allow the wire that is connected with large electric current vertically pass the center of coil, the variation of the magnetic flux that produces by tested current－carrying conductor induces the measurement mechanism that can react the voltage signal of tested size of current.The voltage signal that secondary side induces is the micro component of the large electric current of primary side, so Luo-coil has derivative characteristic.
In tranformer protection of today, because differential protection performance is good, and some other advanced resist technology cost is high, and it is difficult to realize, so differential protection is the main salvo of present transformer.
Transformer can produce excitation surge current when idle-loaded switching-on, the distortion current when this shoves and breaks down with transformer has false similarity, causes easily the relay equipment malfunction.Therefore need to differentiate with fault current shoving.The method of comparative maturity has at present: the method for quadratic harmonics; The balancing waveform method; Interval angle detection method etc.
Because the work magnetic of transformer core properties of materials, iron core is close, the switching angle when saturation magnetic induction, remanent magnetism, air-drop etc. (wherein remanent magnetism and switching angle are at random), all can affect in various degree transformer magnetizing current and distort.Therefore, the distortion degree of shoving is not unique, and the characteristic quantity that needs to detect also is uncertain.Although other harmonic wave proportions are larger relatively for the shared first-harmonic ratio of second harmonic in the excitation surge current, have uncertainty, can change within the specific limits.In the lower situation of the degree of shoving, the very low situation of secondary harmonic component might occur, thereby easily cause the protective device malfunction.
The definite value of interval angle generally is taken between 60 degree-70 degree, and this can only guarantee that the close ratio of saturation magnetic induction and work magnetic is 1.1-1.3, and remanent magnetism is 0.5 left and right sides Shi Keyong.Interval angle is also very large with the variation of excitation factors vary in fact, sometimes may almost not have the appearance of interval angle.Waveform symmetry can only be applied in the even-order harmonic braking that occurs in the symmetrical situation of shoving, in some specific situation, just can occur, and when overexcitation appears in transformer, though its excitation current waveform is symmetrical, also can't differentiate excitation surge current with the waveform symmetry method.In a word, the distortion that present the whole bag of tricks all only shoves from some aspects reflection of current distortion degree, therefore the distortion situation that does not have comprehensively reflection to shove all has obvious limitation, and redundance is lower, malfunction or action delay occur easily.
Summary of the invention
The objective of the invention is: for the limitation of above-mentioned existing inrush current of transformer Distortion Detect method existence; propose a kind ofly can reflect the distortion degree of shoving, the inrush current of transformer Distortion Detect method based on Luo-coil that redundance is high more comprehensively, thereby significantly improve the differential protection performance factor.
In order to achieve the above object, the applicant is carrying out finding behind the off-line analysis to the transformer excitation flow recorder data, when adopting Fourier transform (FFT) to ask the effective value of each harmonic, carry out again Fourier transform behind the first differential if will shove, find that then the effective value of nth harmonic is extended n times.Associate thus.The differentiation of shoving when if the harmonic wave effective value that utilizes extended carries out transient state, then the redundance of criterion will significantly improve, again in conjunction with the derivative characteristic of Luo-coil, namely utilize Luo-coil that the large electric current of transformer primary side is measured, harmonic wave to the differentiated voltage signal that obtains carries out multianalysis, new criterion as inrush current of transformer is differentiated then can reach the foregoing invention purpose in theory.
On this understanding basis, the inrush current of transformer Distortion Detect method based on Luo-coil that the applicant proposes may further comprise the steps:
The first step, by Luo-coil measuring transformer primary side current i (t), obtain differential voltage simulating signal u (t);
Second step, differential voltage simulating signal u (t) carried out analog to digital conversion and filtering process, obtain corresponding differential voltage digital signal u (n) (n=1 ..., N; According to the requirement of existing sampling precision, the value of N generally is taken as 20, i.e. 20 points of a cycle sampling);
The 3rd step, according to the criterion of in the differential protection abnormal current being judged (usually when difference of phase currents greater than 0.5I Cd---I CdBe differential definite value, the stream of perhaps being on duty is greater than 0.8I Cd, judge that then abnormal current appears in transformer), judge whether to occur abnormal current, then carry out in this way next step, as otherwise return the first step;
The 4th step, from first cycle after abnormal current occurring, differential voltage digital signal u (n) is processed through the Fourier transform that adds Cosine Window, obtain each harmonic effective value U i k(i=1,2 ..., m; K=1 ..., N/2), with harmonic wave effective value U i kThe substitution following formula calculates degree of distortion R:
R = ( 1 / i ) * Σ i = 1 m ( Σ k = 2 N / 2 U i k * N U i ) 2
In the formula: U i k(i=1 ..., m; K=1 ..., the k subharmonic effective value of i cycle u of differentiated voltage signal (n) when N/2) being transient state;
N is the sampling number of a cycle;
U iIt is the first-harmonic effective value of i cycle;
There is the cycle number (because the decay of transformer transient state obviously, so m is front m the cycle that has obvious transient state situation, the value of m generally is taken as 3) of harmonic wave in m when being transient state;
The 5th step, judge whether to occur shoving according to degree of distortion R, when R then is judged to be excitation surge current greater than threshold values, then be judged to be internal fault (threshold values differentiated of the degree of distortion of shoving can obtain through experiment, repeatedly experimental verification to try to achieve be 12.5) less than threshold values.
The present invention adopts fast Fourier (FFT) algorithm that adds the Cosine Window interpolation accurately to obtain the effective value of i cycle k of differentiated voltage signal flow control subharmonic, asks the harmonic wave total amount again
Figure GDA0000093117400000032
With first-harmonic effective value U iRatio, this ratio is the degree of distortion R that shoves of i cycle i
Figure GDA0000093117400000033
Then to R i(i=1,2 ..., m) ask root-mean-square value R, the degree of distortion value of shoving when namely defining transient state with the value of R.The high real-time of considering transformer differential protection requires and the quick characteristics that decay of excitation surge current, and when choosing unusual cycle data window (the 4th step was chosen unusual cycle data window), the data of choosing first three cycle are comparatively suitable.
Compared with prior art, remarkable substantive distinguishing features one of the present invention is by the large current signal of Luo-coil measuring transformer primary side, obtain reacting the differentiated voltage signal of large current signal characteristic, this voltage signal is carried out frequency analysis, the numerical value of harmonic content effective value is enlarged redundance and its validity of enhancing of criterion; The 2nd, adopt Fast Fourier Transform (FFT) (FFT) algorithm that adds Cosine Window accurately to calculate the effective value of each harmonic, this algorithm is a kind of improvement algorithm that proposes for the not high shortcoming of conventional fast Fourier transform (FFT) algorithm accuracy; The 3rd, finally determine the degree of distortion value of shoving with mean square root method, can effectively reduce the error of calculation.
When abnormal current was fault current, because harmonic content is minimum, ratio R can be very little, and can not become multiple to change for harmonic wave effective value before and after the differential, so substantially constant through the each harmonic effective value behind the Luo-coil differential; When being excitation surge current, contain a large amount of integral frequency harmonizing waves, the R value will be very large, for the micro component behind the process Luo-coil differential, the nth harmonic effective value of its nth harmonic effective value before than differential enlarges n doubly, and the degree of distortion value of shoving that then obtains will enlarge several times (value through evidence R will enlarge 3-4 times); Therefore being easy to distinguish transformer current according to the size of degree of distortion R is fault electric current or excitation surge current when unusual.And degree of distortion R has reflected the distortion degree of inrush current of transformer all sidedly; therefore can guarantee reliably differential protection not malfunction when transformer during no-load closing; and strictly distinguish exciting current and fault current; criterion value has very high redundance; judge accurately reliably, so the present invention has outstanding progress.
Description of drawings
The present invention is further illustrated below in conjunction with accompanying drawing.
Fig. 1 is the system flowchart of one embodiment of the invention.
Fig. 2 is three-phase and door mode of braking structural representation.
Fig. 3 is one of sampled data oscillogram before the differential.
Fig. 4 is one of harmonic wave effective value chart of first three unusual cycle before the differential.
Fig. 5 is for adding one of Luo-coil differential post-sampling data waveform figure.
Fig. 6 is one of harmonic wave effective value chart of first three unusual cycle behind the differential.
Fig. 7 is two of the front sampled data oscillogram of differential.
Fig. 8 be unusual rear first, second and third cycle harmonic wave effective value chart two.
Fig. 9 is for adding two of Luo-coil differential post-sampling data waveform figure.
Figure 10 be first three unusual cycle behind the differential harmonic wave effective value chart two.
Embodiment
Embodiment one
Present embodiment based on the main flow process of the inrush current of transformer Distortion Detect method of Luo-coil as shown in Figure 1, calculate output element by Luo-coil measurement links, analog to digital conversion and filtering link, the degree of distortion and consist of.The concrete steps of each link are as follows:
1, adopt Luo-coil at measuring section, the large current i of measuring transformer primary side (t) obtains differentiated voltage signal u (t);
2, u (t) is sent into analog to digital conversion and filtering (with prior art roughly the same, the method for existing many maturations is not given unnecessary details in addition) link obtain after processing digital signal u (n) (n=1 ..., N; The sampling number of a cycle of N);
3, judge whether to occur abnormal current according to the criterion of in the differential protection abnormal current being judged, the calculating link that then enters following the 4th step if there is abnormal current, when difference of phase currents greater than 0.5I Cd(I CdBe differential definite value), the stream of perhaps being on duty is greater than 0.8I Cd, judge that then abnormal current appears in transformer;
4, u (n) process is added the Fourier transform of Cosine Window, obtain each harmonic effective value U i k(i=1,2 ..., m; K=1 ..., N/2), with harmonic wave effective value U i kCalculate degree of distortion R in the substitution degree of distortion solution formula.
The high real-time of considering transformer differential protection requires the quick Decay Rate with transformer excitation flow, first three cycle that occurs according to shoving is relatively more abundant and comprehensive to the harmonic information reaction, in the practice of differential protection, only the unusual sampled data that rear first three cycle occurs of intercepting is calculated; Sample frequency is 1000HZ in transformer differential protection, and namely sampling number is 20 points, and this is enough to satisfy the poor guarantor's of transformer calculation requirement.For the cycle be the excitation surge current of 20 sampled points, the value of its higher hamonic wave is in fact very little, obtains the effective value of front 10 subharmonic according to Fast Fourier Transform (FFT), only gets final product with getting 2-10 time so participate in the harmonic wave effective value of computing, then the value of R:
R = ( 1 / 3 ) * Σ i = 1 3 ( Σ k = 2 10 U i k * 20 U i ) 2
Try to achieve through a large amount of emulation and tests:
The threshold limit value value of R can get 12.5, namely is judged as excitation surge current when R＞12.5, is judged as fault current when R＜12.5.
As shown in Figure 2, can adopt three-phase AND gate mode of braking to carry out the differential protection of Three-Phase Transformer, can guarantee that like this transformer main protection can malfunction when air-drop.Ra, rb, rc are respectively A, B, the C three phase excitation judged result of shoving among the figure, r be ra, rb, rc phase and result's (rc is true or false according to the judged result value of A, B, C three-phase for ra, rb).
The below describes as an example of two groups of real recorder datas example.
Fig. 3 to Fig. 6 is that the recorder data behind the flat IB3 phase excitation surge current of stubble unusual is analyzed.Wherein Fig. 3, Fig. 4 calculate the degree of distortion: the R=25.94 that shoves by degree of distortion computing formula of the present invention; Fig. 5, Fig. 6 calculate the degree of distortion: the R=81.08 that shoves by degree of distortion computing formula of the present invention
Fig. 7 to Figure 10 is the recorder data analysis of Yinchuan new city fault current after unusual.Wherein Fig. 7, Fig. 8 draw degree of distortion value: the R=1.92 that shoves after calculating through the present invention; Fig. 9, Figure 10 draw degree of distortion value: the R=1.68 that shoves after calculating through this algorithm.
Can prove that thus the method for present embodiment is practical, have enough validity and reliabilities.
In addition to the implementation, the present invention can also have other embodiments.All employings are equal to the technical scheme of replacement or equivalent transformation formation, all drop on the protection domain of requirement of the present invention.

Claims (4)

1. inrush current of transformer Distortion Detect method based on Luo-coil is characterized in that may further comprise the steps:
The first step, by Luo-coil measuring transformer primary side current
Figure DEST_PATH_IMAGE002A
, obtain the differential voltage simulating signal
Second step, to the differential voltage simulating signal Carry out analog to digital conversion and filtering and process, obtain corresponding differential voltage digital signal
Figure DEST_PATH_IMAGE006AAAA
Figure DEST_PATH_IMAGE008A
The 3rd step, according to the criterion of in the differential protection abnormal current being judged, judge whether to occur abnormal current, then carry out in this way next step, as otherwise return the first step; When difference of phase currents greater than 0.5
Figure DEST_PATH_IMAGE010AAA
, the stream of perhaps being on duty is greater than 0.8
Figure DEST_PATH_IMAGE010AAAA
, judge that then abnormal current appears in transformer;
Figure DEST_PATH_IMAGE010AAAAA
Be differential definite value;
The 4th the step, from first cycle after abnormal current occurring, with the differential voltage digital signal
Figure DEST_PATH_IMAGE006AAAAA
Process through the Fourier transform that adds Cosine Window, obtain the each harmonic effective value
Figure DEST_PATH_IMAGE012AAA
, with the harmonic wave effective value
Figure DEST_PATH_IMAGE012AAAA
The substitution following formula calculates the degree of distortion
Figure DEST_PATH_IMAGE014AAA
:
Figure 405519DEST_PATH_IMAGE016
In the formula:
Figure DEST_PATH_IMAGE012AAAAA
(
Figure DEST_PATH_IMAGE018A
) differentiated voltage signal when being transient state Individual cycle
Figure DEST_PATH_IMAGE022A
The subharmonic effective value;
It is the sampling number of a cycle;
Figure DEST_PATH_IMAGE026A
Be
Figure DEST_PATH_IMAGE028A
The first-harmonic effective value of individual cycle;
The cycle number that has harmonic wave during for transient state;
The 5th the step, according to the degree of distortion
Figure DEST_PATH_IMAGE014AAAA
Judge whether to occur shoving, when
Figure DEST_PATH_IMAGE014AAAAA
Then be judged to be excitation surge current greater than threshold values, then be judged to be internal fault less than threshold values.
2. the inrush current of transformer Distortion Detect method based on Luo-coil according to claim 1 is characterized in that: described differential voltage digital signal
Figure DEST_PATH_IMAGE006AAAAAAA
In , described
Figure DEST_PATH_IMAGE024AAA
Value be taken as 20.
3. the inrush current of transformer Distortion Detect method based on Luo-coil according to claim 2 is characterized in that: the cycle number that has harmonic wave during described transient state
Figure DEST_PATH_IMAGE030AAA
Value be taken as 3.
4. the inrush current of transformer Distortion Detect method based on Luo-coil according to claim 3 is characterized in that: the threshold values that the described degree of distortion of shoving is differentiated is 12.5.
CN 201110224368 2011-08-05 2011-08-05 Method for detecting inrush current distortion of transformer based on Rogowski coil Expired - Fee Related CN102323503B (en)

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CN102798785B (en) * 2012-09-06 2015-05-06 南京南电继保自动化有限公司 Detection method for inrush current differential harmonic of transformer
CN103869180B (en) * 2012-12-18 2017-03-01 施耐德电器工业公司 Prediction with CT saturation under echo surge current and detection method
CN103149470B (en) * 2013-01-29 2015-04-22 北京信息科技大学 Method of distinguishing transformer magnetizing rush current by transformer winding vibration
CN104410044B (en) * 2014-12-02 2017-05-24 国家电网公司 Identification method for excitation surge current of transformer based on kurtosis and skewness
CN107765076B (en) * 2016-08-19 2021-01-15 中国电力科学研究院 Magnetizing inrush current identification method and device
CN106597181B (en) * 2017-02-13 2023-06-02 云南电网有限责任公司电力科学研究院 Operation monitoring system and method for high-voltage power transformer
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