CN111596164A - Single-phase earth fault positioning method based on Pearson correlation coefficient - Google Patents
Single-phase earth fault positioning method based on Pearson correlation coefficient Download PDFInfo
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- CN111596164A CN111596164A CN201910787112.9A CN201910787112A CN111596164A CN 111596164 A CN111596164 A CN 111596164A CN 201910787112 A CN201910787112 A CN 201910787112A CN 111596164 A CN111596164 A CN 111596164A
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- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
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Abstract
The invention discloses a single-phase earth fault positioning method based on Pearson correlation coefficient, which comprises the following steps of providing a data acquisition unit for acquiring zero sequence voltage U when a fault occurs0(t) and zero sequence current I0(t); step two, calculating the zero sequence voltage U according to the derivation formula of the center difference method0Derivative of (t) U'0(t); step three, calculating a zero sequence voltage derivative U 'according to a Pearson correlation coefficient calculation formula based on statistics'0(t) and zero sequence current I0(t) a similarity ρ; and step four, determining whether the section is a fault section or not according to the calculated similarity rho. The invention can eliminate the error caused by the asymmetry of the data center to the similarity calculation and improve the calculated similarity value, thereby being capable of setting the threshold value more easily and improving the upper limit of judging the high-resistance grounding fault. In addition, the method has self-owned performance, can judge the in-situ mode, and reduces the requirement on the synchronism of the equipment at different positions.
Description
Technical Field
The invention relates to the field of distribution network automation systems, in particular to a single-phase earth fault positioning method based on Pearson correlation coefficients.
Background
The domestic power distribution network system mainly adopts an operation mode that a neutral point is not effectively grounded, wherein the operation mode that the neutral point is not grounded is taken as a main mode, and most faults of the system are single-phase grounding faults. When a fault occurs, the fault current is very small, and the waveform of the fault current is seriously distorted due to the instability of the grounding arc, so that the fault is difficult to be positioned by the complex waveform, and the fault positioning can be performed only by a manual wire pulling mode. In recent years, however, with the increase of the requirement for the power supply reliability of the power system, the development of data acquisition technology and theoretical research on low-current ground faults, researchers have made breakthrough progress in the single-phase ground fault location of such systems.
For a single-phase earth fault positioning method of a neutral point ungrounded system, a fault positioning method based on similarity is one of simple, practical and reliable fault positioning methods, the method positions faults by calculating the similarity between a zero-sequence voltage derivative and a zero-sequence current or the similarity between two adjacent zero-sequence currents, wherein for the calculation of the similarity, a cosine similarity calculation formula is mainly adopted for calculation at present. However, due to the influence of sampling errors of the device, the acquired zero-sequence voltage or zero-sequence current data center is asymmetric and deviates upwards or downwards, and at this time, the similarity calculated according to the cosine similarity calculation formula is inaccurate, so a more accurate similarity calculation method is needed, and the error caused by the similarity calculation due to the central asymmetry can be eliminated.
Disclosure of Invention
The invention aims at the problems and overcomes the defects of the prior art, and provides a single-phase earth fault positioning method based on a Pearson correlation coefficient. The method can eliminate similarity calculation errors caused by zero-sequence voltage or zero-sequence current data center asymmetry, and can improve the calculated similarity to a certain extent, so that the threshold value of fault location is easier to set, and the upper limit of high-resistance grounding which can be judged by the method is improved. Meanwhile, the method adopts a center difference method to calculate the derivative of the zero sequence voltage, and the calculation result is more accurate. In addition, the method has self-owned performance, can carry out on-site fault judgment, does not need to upload a large amount of data, reduces the burden of a communication system, and has low requirement on time synchronization among different devices.
The invention positions the fault section by calculating the similarity between the zero sequence voltage derivative and the zero sequence current. The method comprises the steps of firstly conducting derivation on zero-sequence voltage according to a center difference method, then solving the similarity between the zero-sequence voltage derivative and zero-sequence current according to a Pearson correlation coefficient calculation formula in statistics, and finally locating faults according to the similarity obtained through calculation.
In order to achieve the purpose of the invention, the invention adopts the following technical scheme:
a single-phase earth fault positioning method based on Pearson correlation coefficient comprises the following steps,
step one, providing a data acquisition unit for acquiring zero sequence voltage U when a fault occurs0(t) and zero sequence current I0(t)。
Step two, calculating the zero sequence voltage U according to the derivation formula of the center difference method0Derivative of (t) U'0(t)。
Step three, calculating a zero sequence voltage derivative U 'according to a Pearson correlation coefficient calculation formula in statistics'0(t) and zero sequence current I0The similarity ρ of (t).
And step four, determining whether the section is a fault section or not according to the calculated similarity rho.
The derivation formula of the center difference method in the second step is,
wherein, U'0(n) is the derivative of the nth sample point, U0(n +1) is the zero sequence voltage value of the (n +1) th sampling point, U0And (n-1) is the zero sequence voltage value of the n-1 sampling point, and Ts is the sampling period.
The pearson correlation coefficient in step three is calculated as,
wherein i0(n) is the zero sequence current value of the nth point,
is the mean value of the zero sequence current, U'0(n) is the zero sequence voltage derivative value of the nth point,
and N is the data length used for calculating the similarity.
The process of determining whether the section is a fault section in the fourth step is that through test analysis of a large amount of field data, a proper negative threshold value is set for the similarity, when the calculated similarity is smaller than the negative threshold value, the detection point is located in the fault area, and when the calculated similarity is larger than the negative threshold value, the detection point is located outside the fault area.
The invention has the beneficial effects that: according to the single-phase earth fault positioning method based on the Pearson correlation coefficient, whether the fault section is the fault section or not is accurately judged according to the similarity between the zero-sequence voltage derivative and the zero-sequence current obtained through calculation, errors caused by the calculation of the similarity of data without centrosymmetry can be eliminated, the similarity value obtained through calculation is improved, therefore, a threshold value can be set more easily, and meanwhile, the upper limit of high-resistance earth fault judgment can be improved. In addition, the method is self-owned, and can carry out in-situ judgment, so that the requirement on the time synchronization precision among various devices is not very high.
Drawings
Fig. 1 is a general flow chart of the fault location method of the present invention.
Fig. 2 shows waveforms of zero-sequence voltage, zero-sequence voltage derivative and zero-sequence current in case 1 of the present invention.
Fig. 3 shows waveforms of zero sequence voltage, zero sequence voltage derivative and zero sequence current in case 2 of the present invention.
Fig. 4 shows waveforms of zero sequence voltage, zero sequence voltage derivative and zero sequence current in case 3 of the present invention.
Fig. 5 shows waveforms of zero sequence voltage, zero sequence voltage derivative and zero sequence current in case 4 of the present invention.
Fig. 6 shows waveforms of zero-sequence voltage, zero-sequence voltage derivative and zero-sequence current in case 5 of the present invention.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and examples to specifically illustrate the technical solutions of the present invention. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
A single-phase earth fault positioning method based on Pearson correlation coefficient comprises the following steps,
step one, providing a data acquisition unit for acquiring zero sequence voltage U when case 1-case 5 faults occur0(t) and zero sequence current I0The waveforms of (t) data are shown in fig. 2 to 6, respectively.
Step two, respectively calculating the zero sequence voltage U acquired in cases 1 to 5 according to the derivation formula of the center difference method0Derivative of (t) U'0(t) waveforms of which are shown in FIGS. 2 to 6, respectively, and a derivation formula in the center difference method is,
wherein, U'0(n) is the derivative of the nth sample point, U0(n +1) is the zero sequence voltage value of the (n +1) th sampling point, U0And (n-1) is the zero sequence voltage value of the n-1 sampling point, and Ts is the sampling period.
Step three, respectively calculating the similarity between the zero-sequence voltage derivative and the zero-sequence current in cases 1 to 5 according to a Pearson correlation coefficient calculation formula in statistics, wherein the Pearson correlation coefficient calculation formula is as follows,
wherein i0(n) is the zero sequence current value of the nth point,
is the mean value of the zero sequence current, U'0(n) is the zero sequence voltage value of the nth point,
and N is the data length used for calculating the similarity.
And step four, determining whether the areas where the detection points in cases 1 to 5 are located are fault sections according to the calculated similarity. Firstly, through test analysis of a large amount of field data, setting a proper negative threshold value of-0.6 for the similarity, wherein the similarity obtained by calculation by adopting a Pearson correlation coefficient formula in case 1 is-0.7200 and is obviously smaller than the threshold value, judging that the detection point is positioned in a fault area, and the similarity obtained by calculation by adopting a cosine similarity formula is-0.6055, so that misjudgment is easily caused at the edge of the threshold value; in case 2, the similarity calculated by adopting the pearson correlation coefficient calculation formula is-0.7571, and the similarity calculated by adopting the cosine similarity formula is-0.6621, so that the similarity is improved by 14 percent and is more obviously smaller than a threshold value of-0.6, and a detection point is judged to be in a fault area when the fault occurs; in case 3, the similarity obtained by calculating the Pearson correlation coefficient is-0.8572, the similarity obtained by calculating the cosine similarity formula is-0.8172, the similarity is improved by 5 percent and is smaller than a negative threshold value of-0.6, and the detection point is determined to be in a fault area when the fault occurs; in case 4, the similarity obtained by calculating the pearson correlation coefficient is-0.8603, and the similarity obtained by calculating the cosine similarity formula is-0.6946, so that the similarity is improved by 24 percent, the similarity is greatly improved and is more obviously smaller than a negative threshold value of-0.6, and the detection point is judged to be in a fault area when the fault occurs; in case 5, the similarity obtained by calculating the pearson correlation coefficient is 0.6656, and the similarity obtained by calculating the cosine similarity formula is 0.5601, so that the similarity is improved by 19 percent and is more obviously greater than a negative threshold value of-0.6, and the detection point is outside the fault area when the fault occurs.
In this embodiment: and verifying the fault positioning method by using actual field data. As can be seen from fig. 2, the fault is a high-resistance ground fault of a voltage zero crossing point, and has no transient characteristic, and the steady state value of the zero-sequence current is small, and the waveform overall deviates upwards, and it is difficult to locate the fault by using the conventional method, but when the similarity is calculated by using the cosine similarity formula, the obtained similarity is at the threshold boundary, which is easy to cause misjudgment, and when the similarity is calculated by using the pearson correlation coefficient calculation formula, the similarity is significantly improved, and is significantly smaller than the threshold, which does not cause misjudgment. Case 2 is one-time arc grounding, the waveform of the second half section of the waveform is wholly deflected downwards, and the similarity is obviously improved by adopting a similarity calculation formula of the Pearson correlation coefficient, so that the threshold value is easier to set. Case 5 is a one-time intermittent earth fault, and the similarity obtained by calculation is greatly improved by adopting a similarity calculation formula of the Pearson correlation coefficient.
In summary, the invention provides a single-phase earth fault location method based on pearson correlation coefficient, which first derives the zero-sequence voltage according to the derivation formula of the center difference method, then calculates the similarity between the zero-sequence voltage derivative and the zero-sequence current according to the pearson correlation coefficient calculation formula in statistics, and finally determines whether the fault section is the fault section according to the calculated similarity. The method can accurately position the fault section, eliminates the influence of asymmetry of the data center on similarity calculation, improves the calculated similarity, and improves the upper limit of high-resistance grounding judgment.
The above embodiments are illustrative of specific embodiments of the present invention, and are not restrictive of the present invention, and those skilled in the relevant art can make various changes and modifications without departing from the spirit and scope of the present invention to obtain corresponding equivalent technical solutions, and therefore all equivalent technical solutions should be included in the scope of the present invention.
Claims (4)
1. A single-phase earth fault positioning method based on Pearson correlation coefficient is characterized in that: comprises the following steps of (a) carrying out,
step one, providing a data acquisition unit for acquiring zero sequence voltage U when a fault occurs0(t) and zero sequence current I0(t)；
Step two, calculating the zero sequence voltage U according to the derivation formula of the center difference method0Derivative of (t) U'0(t)；
Step three, calculating a zero sequence voltage derivative U 'according to a Pearson correlation coefficient calculation formula in statistics'0(t) and zero sequence current I0(t) a similarity ρ;
and step four, determining whether the section is a fault section or not according to the calculated similarity rho.
2. The single-phase earth fault positioning method based on the pearson correlation coefficient as claimed in claim 1, wherein: in the second step, the zero sequence voltage U is calculated according to the derivation formula of the center difference method0Derivative of (t) U'0(t), the derivation formula of the center difference method is,
wherein, U'0(n) is the derivative of the nth sample point, U0(n +1) is the zero sequence voltage value of the (n +1) th sampling point, U0And (n-1) is the zero sequence voltage value of the n-1 sampling point, and Ts is the sampling period.
3. The single-phase earth fault positioning method based on the pearson correlation coefficient as claimed in claim 1, wherein: calculating zero sequence voltage derivative U 'in step three'0(t) and zero sequence current I0(t) similarity, wherein the Pearson's correlation coefficient in statistics is calculated as,
wherein i (n) is the zero sequence current value of the nth point,
is the mean value of the zero sequence current, U'0(n) is the zero sequence voltage derivative value of the nth point,
and N is the data length used for calculating the similarity.
4. The single-phase earth fault positioning method based on the pearson correlation coefficient as claimed in claim 1, wherein: the process of determining whether the section is a fault section in the fourth step is that through test analysis of a large amount of field data, a proper negative threshold value is set for the similarity, when the calculated similarity is greater than the negative threshold value, the detection point is located in the fault area, and when the calculated similarity is greater than the negative threshold value, the detection point is located outside the fault area.
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| CN112731240A (en) * | 2020-12-21 | 2021-04-30 | 青岛鼎信通讯股份有限公司 | Ground fault positioning method applied to fault indicator |
| CN113376534A (en) * | 2021-05-12 | 2021-09-10 | 山东大学 | Phase plane diagnosis method for early fault of power battery and advanced early warning system |
| CN113484673A (en) * | 2021-06-29 | 2021-10-08 | 中国矿业大学 | Single-phase arc grounding fault section positioning method based on zero-mode component similarity |
| CN113866568A (en) * | 2021-12-02 | 2021-12-31 | 青岛鼎信通讯股份有限公司 | Single-phase earth fault positioning method applied to electric power field |
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