Power distribution network fault line selection method based on improved Bhattacharyya distance algorithm

Abstract

The invention relates to the technical field of power distribution network grounding fault line selection, in particular to a power distribution network fault line selection method based on an improved Bhattacharyya distance algorithm, and the method comprises the steps: converting a transient zero-sequence current signal of a first 1 / 4 power frequency period of each line after a fault into a polar coordinate form through Hilbert conversion; taking the amplitude and the phase of the signal as two variables of polar coordinates, and constructing a discrete probability distribution function of any two lines; calculating an average BD value between any line and other lines based on an improved Bhattacharyya distance calculation formula; and taking the average BD value as a fault line selection criterion, selecting the lines with the first s average BD values as suspected fault lines, and if the phase intervals with the maximum signal sampling points of the s lines are consistent, judging that the bus fault occurs in the power system, otherwise, judging that the line with the maximum average BD value is the fault line. According to the method, two dimension features of phase and amplitude are introduced, and the accuracy of judging the fault state of the power system line is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network grounding fault line selection, and more specifically, to a distribution network fault line selection method based on an improved Bhattacharyya distance algorithm. Background Art

[0002] The active intelligent distribution network under the background of the new power system is an important part of the smart grid. Compared with the traditional distribution network, a large number of power electronic devices with different functions such as new energy power generation, energy storage, and electric vehicles are connected to the new distribution network, making the grid structure, operation mode, and fault signals all show new characteristics different from those of the traditional distribution network. The distribution network is no longer just a provider of unidirectional electric energy, but is transforming into a more advanced new distribution network role. There are many new characteristics in the electrical signals in the new distribution network, which exacerbate the difficulties in detecting, locating, isolating, and restoring control of the fault characteristics of the new distribution network.

[0003] The distribution network system has a wide erection range and complex line types, which is a weak link in the power system. At present, the single-phase grounding fault identification and location technology in the distribution network has poor adaptability to the distribution network with complex and changeable operating environments. The causes of single-phase grounding faults are diverse, and there are a large number of types of grounding faults such as instantaneous high resistance, intermittent arc, weak transient signals, and strong noise backgrounds. The identification and location of single-phase grounding faults have always been a technical difficulty. When high-resistance and arc grounding faults occur, it faces the dead zone of zero-sequence protection, causing extended hazards such as multi-point grounding, phase-to-phase short circuit, insulation breakdown and burning of cables and neutral point small resistors, etc. Therefore, the effective diagnosis and location of grounding faults are the key to improving the power supply reliability and safety of the new distribution network.

[0004] While the scale and structure of the distribution network are becoming more and more complex, the difficulty of fault line selection is also continuously increasing. On the one hand, the running time of the algorithm increases, and the speed of fault line selection slows down, failing to meet the real-time requirements of distribution network fault location. On the other hand, the algorithms applied to distribution network fault line selection are gradually increasing, but some algorithms have many problems in adaptability under the conditions of changing protection and location coordination mechanisms in different distribution network topologies and different fault types. Therefore, considering the actual working conditions of the distribution network, establishing a fault isolation mechanism with self-adaptive correction characteristics and finding or constructing the most suitable fault line selection algorithm have become technical problems that need to be solved urgently by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a distribution network fault line selection method based on an improved Bhattacharyya distance algorithm, introducing two-dimensional features of phase and amplitude to improve the judgment accuracy of the fault state of power system lines.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A fault line selection method for distribution networks based on an improved Bhattacharyya distance algorithm, comprising the following steps:

[0008] S1. Transform the transient zero-sequence current signals of each line in the first 1 / 4 power frequency cycle after the fault into polar coordinate form through Hilbert transform; use the amplitude and phase of the signals as the two variables of the polar coordinates to construct the discrete probability distribution functions of any two lines;

[0009] S2. Calculate the average BD value between any line and other lines based on the improved Bhattacharyya distance calculation formula;

[0010] S3. Use the average BD value as the fault line selection criterion, select the top s lines with the highest average BD values as suspected fault lines. If the phase intervals with the most signal sampling points of the s lines are the same, it is determined that a bus fault has occurred in the power system; otherwise, the line with the largest average BD value is determined as the fault line.

[0011] Further, in S1, for any two lines in the power system, let the maximum amplitude b and the minimum amplitude a of the two lines be used as the amplitude interval range, form a circular ring in the complex plane, and divide the circular ring into m small circular rings with equal areas; the range of the phase is (-π, π], and the phase is divided into n intervals every θ angle, forming n×m intervals with equal areas.

[0012] Further, in S1, set the number of amplitude intervals m according to the maximum amplitude σ of the zero-sequence current of the fault line and the ratio K of the power system voltage to the 10 kV distribution network voltage. m is taken according to the following formula:

[0013]

[0014] Further, in S1, by reducing the amplitude interval range and increasing the number of amplitude intervals, the discrete probability distribution functions p(x) and q(x) of the signals of the two lines are reduced to reduce the Bhattacharyya coefficient BC and increase the Bhattacharyya distance BD value, so as to distinguish the fault line from the healthy line.

[0015] Further, in S2, the improved Bhattacharyya distance calculation formula is:

[0016]

[0017] where p(γ i , θ j ), q(γ i , θ j ) are two-dimensional probability distribution functions, and their values are the proportions of the sampling points of the two zero-sequence current sampling points falling into the i-th amplitude interval γ i and the j-th phase interval θ j in the total number of sampling points; m represents the number of amplitude intervals; n represents the number of phase intervals.

[0018] Further, in S2, the BD value matrix D of all lines is expressed as:

[0019]

[0020] where BD ij is the BD value between line i and line j.

[0021] Further, in S2, the calculation formula for the average BD value between any line and other lines is:

[0022]

[0023] where BD n is used to reflect the similarity degree of the amplitude and phase between line n and other lines; l represents the other l lines except the current line n.

[0024] Further, in S3, the process of fault line selection based on the average BD value includes:

[0025] Select the top three lines with the highest average BD values in descending order of the average BD value as the suspected fault lines;

[0026] When a line fails, the polarities of the fault line and the sound line are opposite. At this time, the phase intervals with the most sampling points of the two are different. Introduce the polarity discrimination parameter H. When the phase intervals with the most signal sampling points of line i and line j are the same, let H ij = 0, and when the phases are different, let H ij = 1;

[0027] If the sum H sum of the H values of the three suspected fault lines is 0, it is determined that a bus fault has occurred in the power system, otherwise it is determined that the line with the largest average BD value is the fault line.

[0028] Further, when the zero-sequence voltage in the power system is greater than 0.15 times the rated voltage, it is determined that there is a fault in the power system. At this time, the fault line selection process of S1 - S3 is automatically started.

[0029] It can be seen from the above technical solutions that compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention improves the original Bhattacharyya distance calculation formula, introduces the characteristics of two dimensions of amplitude and phase, and further realizes the measurement of the probability distributions of two line signals from two aspects of amplitude and phase. When applied to the fault detection of the distribution network, it makes the judgment of the fault state more accurate, thereby improving the accuracy of fault line selection and more quickly isolating and restoring the fault. The present invention will overcome the influence brought by the access of distributed power sources and provide strong support for the distribution network fault self-healing technology under the new power system. Brief Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0032] Figure 1 It is a flowchart of the distribution network fault line selection method based on the improved Bhattacharyya distance algorithm provided by the present invention;

[0033] Figure 2 It is a schematic diagram of the division of the signal amplitude and phase intervals provided by the present invention;

[0034] Figure 3 It is a schematic diagram that after a single-phase ground fault occurs, the zero-sequence current phases of the fault line and the sound line are completely opposite. Detailed Embodiments

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0036] As Figure 1 shown, the embodiment of the present invention discloses a distribution network fault line selection method based on an improved Bhattacharyya distance algorithm, including the following steps:

[0037] S1. Convert the transient zero-sequence current signals of each line in the first 1 / 4 power frequency period after the fault into polar coordinate form through Hilbert transform; use the amplitude and phase of the signal as the two variables of the polar coordinates to construct the discrete probability distribution functions of any two lines;

[0038] S2. Calculate the average BD value between any line and other lines based on the improved Bhattacharyya distance calculation formula;

[0039] S3. Use the average BD value as the fault line selection criterion. Select the s lines with the top-ranked average BD values as the suspected fault lines. If the phase intervals with the most signal sampling points of the s lines are the same, it is determined that a bus fault has occurred in the power system; otherwise, the line with the largest average BD value is determined as the fault line.

[0040] When the zero-sequence voltage U 0 in the power system is greater than 0.15 times the rated voltage U N , it is judged that there is a fault in the power system. At this time, the fault line selection process of S1 - S3 is automatically started.

[0041] Next, the above steps will be further described.

[0042] When using the Bhattacharyya distance measure, first segment the amplitudes of the two signals to obtain the discrete probability distribution functions p(x) and q(x) of the two signals. Their values are the ratios of the number of sampling points in each segment to the total number of sampling points. Finally, calculate the Bhattacharyya coefficient (BC) and the Bhattacharyya distance. The smaller the obtained BD value, the higher the similarity between the two signals. The expressions are shown in Equations (1) and (2) as follows:

[0043]

[0044] BD = -ln(BC) (2);

[0045] The commonly used BD discrimination method only segments the signal amplitudes to obtain the probability distribution function, without considering the influence of the phase distribution. Moreover, when the impedance differences of healthy lines in the power system are large, the Bhattacharyya distance between lines is small, and the line selection accuracy is low. Therefore, the above formula needs to be improved. The specific improvement process includes:

[0046] S1. Polar coordinate interval division.

[0047] The fault information of the transient zero-sequence current in the first 1 / 4 power frequency cycle after the fault is obvious. Use the Hilbert transform to convert the signal in this time period to polar coordinates, with the amplitude and phase of the signal as the two variables of the polar coordinates.

[0048] For any two lines in the power system, let the maximum amplitude b and the minimum amplitude a of the two lines be the amplitude interval range, forming a ring in the complex plane. Divide the ring into m small rings with equal areas; the range of the phase is (-π, π], and the phase is divided into n intervals every θ angle, forming n×m intervals with equal areas.

[0049] The smaller the interval angle θ, the larger the number of intervals n, indicating that the zero-sequence current signal is decomposed more specifically. It is easier to reflect the difference between the fault line and the healthy lines.

[0050] As Figure 2 shown, in the simulation experiment, the amplitude range is divided into two intervals, the amplitude ac interval and the amplitude cb interval, and the angle is divided into eight intervals, each interval being 45°, that is Figure 2 there are a total of 16 interval ranges in

[0051] Under the condition of a low-resistance fault, the amplitude difference between lines is large, so a smaller number of amplitude intervals is set to improve the similarity of healthy lines; while under the condition of a high-resistance fault, the amplitude difference between lines is small, and more amplitude intervals can be set to increase the difference between the faulty line and the healthy lines. Specifically, the number of amplitude intervals m is set according to the maximum amplitude σ of the zero-sequence current of the faulty line and the ratio K of the power system voltage to the 10 kV distribution network voltage. m is taken according to the following formula (3):

[0052]

[0053] When two line signals have the same phase, by reducing the amplitude interval range and increasing the number of amplitude intervals, the discrete probability distribution functions p(x) and q(x) of the two line signals are reduced to reduce the Bhattacharyya coefficient BC and increase the Bhattacharyya distance BD value, so as to clearly distinguish the faulty line from the healthy lines. By increasing the BD value between the line with a smaller line impedance and other lines, the influence of the line impedance on the Bhattacharyya distance discrimination method is further reduced.

[0054] S2. Calculate the average BD value between any line and other lines based on the improved Bhattacharyya distance calculation formula. The improved Bhattacharyya distance calculation formula is as shown in formula (4):

[0055]

[0056] where p(γ i , θ j ), q(γ i , θ j ) is a two-dimensional probability distribution function, and its value is the proportion of the number of sampling points of the two zero-sequence current sampling points falling into the amplitude interval γ i and the phase interval θ j to the total number of sampling points; m represents the number of amplitude intervals; n represents the number of phase intervals.

[0057] Construct the BD value matrix D of all lines, which is expressed as:

[0058]

[0059] where BD ij is the BD value between line i and line j.

[0060] According to the matrix D, the average BD value BD n, BD n It can reflect the similarity degree of the amplitude and phase between line n and other lines. The calculation formula of the average BD value between any line and other lines is shown in Equation (6):

[0061]

[0062] where BD n is used to reflect the similarity degree of the amplitude and phase between line n and other lines; l represents the other l lines except the current line n.

[0063] S3. Fault line selection criterion.

[0064] After obtaining the average BD value of each line, select the top three lines with the highest average BD value as the suspected fault lines in the order from high to low of the average BD value;

[0065] When a line fails, the polarity of the fault line is opposite to that of the healthy line. As Figure 3 shown, after a single-phase ground fault occurs, the zero-sequence current phases of the fault line and the healthy line are completely opposite. Figure 3 In [figure], the red line is the zero-sequence current phase of the fault line, and the blue line is the zero-sequence current phase of the healthy line, with a difference of almost 180°. The sampling intervals are different. At this time, the phase intervals with the most sampling points of the two are different. Introduce the polarity discrimination parameter H. When the phase intervals with the most signal sampling points of line i and line j are the same, let H ij = 0; when the phases are different, let H ij = 1;

[0066] If the sum H sum of the H values of the three suspected fault lines is 0, it is determined that a bus fault occurs in the power system; otherwise, it is determined that the line with the largest average BD value is the fault line.

[0067] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple. For the relevant parts, refer to the description in the method part.

[0068] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for fault line selection in distribution network based on improved Bhattacharyya distance algorithm, characterized in that: The following steps are involved: S1. Convert the transient zero-sequence current signal of the first 1 / 4 power frequency cycle of each line after the fault into polar coordinate form through Hilbert transform; use the amplitude and phase of the signal as two variables of the polar coordinate to construct the discrete probability distribution function of any two lines; S2, calculating the average BD value between any route and other routes based on the improved Bhattacharyya distance calculation formula; S3. Use the average BD value as the fault line selection criterion, and select the lines with the top s average BD values ​​as suspected fault lines. If the phase intervals with the most signal sampling points of the s lines are consistent, it is determined that a bus fault has occurred in the power system. Otherwise, the line with the largest average BD value is determined to be the fault line.

2. The method for fault line selection in distribution network based on improved Bhattacharyya distance algorithm according to claim 1 is characterized in that: In S1, for any two lines in the power system, the maximum amplitude b and the minimum amplitude a of the two lines are set as the amplitude interval range, forming a ring in the complex plane, and dividing the ring into m small rings with equal areas; the phase range is (-π,π], and the phase is divided into n intervals every angle θ, forming n×m intervals with equal areas.

3. The method for fault line selection in distribution network based on improved Bhattacharyya distance algorithm according to claim 2 is characterized in that: In S1, the number of amplitude intervals m is set according to the maximum amplitude of the zero-sequence current σ of the fault line and the ratio K of the power system voltage to the 10kV distribution network voltage. The value of m is determined according to the following formula:

4. The method for fault line selection in distribution network based on improved Bhattacharyya distance algorithm according to claim 1, characterized in that: In S1, by reducing the amplitude interval range and increasing the number of amplitude intervals, the discrete probability distribution functions p(x) and q(x) of the two line signals are reduced to reduce the Bhattacharyya coefficient BC and increase the Bhattacharyya distance BD value, thereby distinguishing the faulty line from the sound line.

5. The method for fault line selection in distribution network based on improved Bhattacharyya distance algorithm according to claim 1, characterized in that: In S2, the improved Bhattacharyya distance calculation formula is: Among them, p(γ i ,θ j ), q(γ i ,θ j ) is a two-dimensional probability distribution function, whose value is the value of the two zero-sequence current sampling points falling into the i-th interval of amplitude γ i and phase j interval θ j The ratio of the number of sampling points to the total number of sampling points; m represents the number of amplitude intervals; n represents the number of phase intervals.

6. The method for fault line selection in distribution network based on improved Bhattacharyya distance algorithm according to claim 1, characterized in that: In S2, the BD value matrix D of all lines is expressed as: Among them, BD ij is the BD value between line i and line j.

7. The method for fault line selection in distribution network based on improved Bhattacharyya distance algorithm according to claim 6 is characterized in that: In S2, the calculation formula for the average BD value between any line and other lines is: Among them, BD n It is used to reflect the similarity between the amplitude and phase of line n and other lines; l represents the other l lines except the current line n.

8. The method for fault line selection in distribution network based on improved Bhattacharyya distance algorithm according to claim 1, characterized in that: In S3, the process of fault line selection based on the average BD value includes: In descending order of average BD values, the top three lines with the highest average BD values ​​are selected as suspected fault lines; When a line fails, the faulty line has the opposite polarity to the healthy line. At this time, the phase intervals with the most sampling points of the two are different. The polarity discrimination parameter H is introduced. When the phase intervals with the most signal sampling points of line i and line j are the same, let H ij =0, when the phase is different, let H ij =1; If the sum of the H values ​​of the three suspected fault lines is sum If it is 0, it is determined that a bus fault occurs in the power system, otherwise it is determined that the line with the largest average BD value is the fault line.

9. The method for fault line selection in distribution network based on improved Bhattacharyya distance algorithm according to claim 1, characterized in that: When the zero-sequence voltage in the power system is greater than 0.15 times the rated voltage, it is determined that there is a fault in the power system. At this time, the fault line selection process of S1-S3 is automatically started.

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