CN113721114B - High-resistance ground fault line selection method, system and storage medium for resonant ground power distribution network - Google Patents
High-resistance ground fault line selection method, system and storage medium for resonant ground power distribution network Download PDFInfo
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Abstract
The invention discloses a high-resistance ground fault line selection method, a system and a storage medium for a resonant ground power distribution network, wherein the method comprises the following steps: acquiring the zero sequence voltage of a bus of the power distribution network, and performing preliminary judgment; then acquiring a zero sequence current sequence of a feeder line on the bus; acquiring a first local extreme point of a waveform after the zero-sequence zero-crossing for the first time and a second local extreme point of the waveform after the zero-sequence current waveform zero-crossing for the second time; taking the central points of the two local extreme points as the centers of the time windows, and solving zero sequence current linearity sequences under different time window widths; the change rate sequence of the zero sequence current linearity sequence is obtained; if the numbers of positive and negative in the change rate sequence are not smaller than the preset number, judging that the feeder line has high-resistance ground fault; otherwise, the feeder line does not have a high resistance ground fault. The high-resistance fault line can be timely and accurately selected, the fault is removed, the long-time operation of the distribution line under the high-resistance fault is avoided, and the safe and reliable operation of the distribution network is ensured.
Description
Technical Field
The invention relates to the technical field of intelligent power distribution, in particular to a high-resistance ground fault line selection method, a high-resistance ground fault line selection system and a storage medium for a neutral point resonance grounding power distribution network.
Background
The medium-voltage distribution network in China widely adopts a grounding mode that a neutral point is not grounded or passes through an arc suppression coil, and is also called as low-current grounding. When a single-phase grounding fault occurs in the low-current grounding system, a short circuit loop is not formed, the grounding fault current is small, line voltages among three phases of the system are basically symmetrical, load power supply cannot be affected, the system can be operated for a period of time with faults, and the power supply reliability is high. But the difficulty of fault detection is increased due to the small single-phase earth fault current.
Because of the drooping or wind blowing of the wire with excessive load, the distribution line is often contacted with branches, bamboos and the like; because of severe weather such as ice and snow or human factors, broken wires of the wires fall on the surface of non-ideal media with high impedance such as asphalt, lawns and the like, and the fault that the wires are contacted with the high-impedance media is called as high-impedance fault. The fault current is small when the resonance grounding system has single-phase grounding fault, and the fault current is smaller when the resonance grounding system has high-resistance grounding fault. When a high-resistance ground fault occurs, the fault resistance reaches hundreds of ohms to tens of thousands of ohms. When a high-resistance fault occurs, such as when a line is grounded through a tree, fault current is weak, the zero-sequence current of the fault line is possibly below 1 ampere, which is equivalent to the zero-sequence current caused by unbalanced line parameters, the conventional method cannot detect and select the line, so that the high-resistance fault exists for a long time and can be extended to be a more serious fault, fire disaster or casualties are caused, and the threat to personal safety and stable operation of a power system is caused. Therefore, an effective method and system for detecting and selecting high-resistance ground faults of a resonant ground system are needed.
Disclosure of Invention
The invention provides a high-resistance ground fault line selection method, a high-resistance ground fault line selection system and a storage medium for a resonant ground power distribution network, which are used for solving the problem that the existing method cannot realize the detection and line selection of the high-resistance ground fault.
In a first aspect, a high-resistance ground fault line selection method for a resonant ground power distribution network is provided, including:
step S1: acquiring the zero sequence voltage of a bus of the power distribution network, if the zero sequence voltage of the bus is larger than a zero sequence voltage setting value, judging that a suspected single-phase earth fault occurs, turning to a step S2, otherwise, repeating the step S1;
step S2: acquiring a zero sequence current sequence { x (n) } of a feeder line on the bus; the zero sequence current sequence { x (N) } is obtained by continuously sampling zero sequence current of one feeder line on a bus for a preset time length at a preset sampling frequency, wherein n=1, 2,3, …, and N are the total number of samples;
step S3: acquiring a first local extreme point x (n) of a waveform after the zero-crossing of the zero-sequence current sequence 1 ) Wherein n is 1 Is the sampling value sequence number of the extreme point; acquiring a second local extreme point x (n) of the waveform after zero-sequence current waveform crosses zero again 2 ) Wherein n is 2 Is the sampling value sequence number of the extreme point;
step S4: to be used forFor the center of the time window, the width of the time window is 2w, wherein round is a rounding function, w is a positive integer smaller than M, and the linearity of the zero sequence current in the time window is obtained; changing the time window width, and obtaining zero sequence current linearity sequences L (w) under different time window widths, wherein w=1, 2,3, …, M-1 and M are preset values;
step S5: the change rate sequence GoL (k) of the zero sequence current linearity sequence is obtained;
step S6: if the numbers of positive and negative values in the change rate sequence GoL (k) are not smaller than the preset number, judging that the feeder line has high-resistance ground faults; otherwise, the feeder line does not have high-resistance ground fault;
step S7: and (2) detecting other feeder lines on the bus by adopting the steps S2 to S6, and judging whether the feeder lines have single-phase high-resistance ground faults or not.
Further, the zero sequence current linearity sequence L (w) in the step S4 is calculated by the following method:
wherein,
further, in the step S5, a 7-point linear fitting method is adopted to calculate a change rate sequence GoL (k) of the zero sequence current linearity sequence, and a calculation formula is as follows:
wherein,k=1, 2,3, …, M-6. The change rate of the curve is obtained by using 7 sampling points through a linear fitting method, the noise immunity is high, the random fluctuation of the change rate when signals are interfered by noise can be avoided, and the line selection accuracy is improved.
Further, the zero sequence voltage setting value in the step S1 is 5% of the nominal value of the phase-taking voltage.
Further, the step S2 is performed with a delay of at least 0.2 seconds before sampling. Compared with the existing line selection method adopting transient signals, the method can avoid the problem that the fault line selection error is caused because the transient process of the high-resistance fault is not obvious and the fault occurrence time is difficult to capture.
Further, the preset sampling frequency in the step S2 is 10kHz, and the preset duration is not shorter than 0.03 seconds. The preset time length is preferably 0.03 seconds, which is 1.5 power frequency periods, and 2 adjacent extreme points meeting the condition can be always found in the 1.5 power frequency periods.
Further, for the first local extremum point and the second local extremum point in the step S3, if the local extremum point is a maximum value, the value of the local extremum point is a maximum value of the continuous Z points centered on the local extremum point; if the local extremum point is a minimum point, the value of the local extremum point is the minimum value of the continuous Z points centered on the local extremum point, wherein the Z value can be 7, 9 or 11.
Further, the value of M in the step S4 is 50 (equal to the sampling point in the half power frequency period), the preset number in the step S6 is 5, the total number of gols (k) is 44, the preset number is an integer greater than 10% of the total number of the elements of the sequence gols (k), and 5 is greater than 10% of the total number of the elements of the sequence gols (k).
In a second aspect, a resonant grounded power distribution network high-resistance ground fault line selection system is provided, including:
the primary judgment module is used for acquiring the zero sequence voltage of the bus of the power distribution network, judging that the power distribution network is suspected of single-phase earth fault if the zero sequence voltage of the bus is larger than a zero sequence voltage setting value, and repeating the judgment process if the power distribution network is not suspected of single-phase earth fault;
the fault detection module is used for respectively detecting high-resistance grounding faults of each feeder line on the bus and judging whether single-phase high-resistance grounding faults occur or not; the fault detection module comprises a sampling unit, a linearity acquisition unit, a change rate acquisition unit and a fault judgment unit; wherein:
the sampling unit is used for acquiring a zero sequence current sequence { x (n) } of one feeder line on the bus; the zero sequence current sequence { x (N) } is obtained by continuously sampling zero sequence current of one feeder line on a bus for a preset time length at a preset sampling frequency, wherein n=1, 2,3, …, and N are the total number of samples;
the linearity obtaining unit is used for obtaining a first local extreme point x (n) of the waveform after the zero-crossing of the zero-sequence current sequence for the first time 1 ) Wherein n is 1 Is the sampling value sequence number of the extreme point; acquiring a second local extreme point x (n) of the waveform after zero-sequence current waveform crosses zero again 2 ) Wherein n is 2 Is the sampling value sequence number of the extreme point; to be used forFor the center of the time window, the width of the time window is 2w, wherein round is a rounding function, w is a positive integer smaller than M, and the linearity of the zero sequence current in the time window is obtained; changing the time window width, and obtaining zero sequence current linearity sequences L (w) under different time window widths, wherein w=1, 2,3, …, M-1 and M are preset values;
the change rate acquisition unit is used for solving a change rate sequence GoL (k) of the zero sequence current linearity sequence;
the fault judging unit is used for judging that the feeder line has high-resistance ground fault when the numbers of positive and negative in the change rate sequence GoL (k) are not smaller than the preset number; otherwise, the feeder line does not have a high resistance ground fault.
In a third aspect, a computer readable storage medium is provided, storing a computer program adapted to be loaded by a processor and to perform a resonant ground distribution network high resistance ground fault line selection method as described above.
Advantageous effects
The invention provides a high-resistance ground fault line selection method, a high-resistance ground fault line selection system and a storage medium for a resonant ground power distribution network, which have the following advantages:
1. the neutral point resonance grounding distribution network high-resistance grounding fault line selection scheme provided by the invention can solve the problems that when the existing resonance grounding system generates single-phase high-resistance grounding faults, the zero sequence current of a fault line is equivalent to the zero sequence current caused by three-phase imbalance of a distribution line, and the conventional method cannot judge whether the high-resistance grounding faults occur or not and cannot effectively select the fault line. The scheme can timely and accurately select the high-resistance fault line, is favorable for removing faults, avoids long-time operation of the distribution line under the high-resistance fault, and ensures safe and reliable operation of the distribution network.
2. According to the invention, the waveform distortion characteristic of the zero sequence current of the fault line when the resonance grounding system generates the high-resistance grounding fault is utilized to obtain the law of the waveform linearity of the zero sequence current along with the length change of the time window. When the power distribution network normally operates, the zero-sequence current zero-crossing point of the circuit is taken as the center of the time window, and the linearity of the current waveform is monotonically decreased or monotonically increased along with the increase of the length of the time window; the linearity of the current waveform changes in a fluctuation manner with the increase of the time window length during the high-resistance ground fault, and the current waveform falls first and then rises or falls first and then falls. And (3) calculating the change rate of the linearity of the zero sequence current waveform along with the length of the time window, wherein the change rate is negative or positive in normal operation, and the change rate is positive or negative in high-resistance fault. By adopting the principle, the high-resistance fault and the unbalanced state of the line can be effectively identified, so that fault line selection is realized.
3. When high-resistance ground faults occur, the nonlinear characteristics of the ground transition resistance are different due to the difference of the ground mediums (branches, mud, roads, sewage and the like), so that the lengths of the flat areas of the zero sequence current waveform distortion are different. The invention utilizes the change rule of the zero sequence current waveform linearity along with the length of the time window to identify waveform distortion and select lines, can not be influenced by the length of a waveform distortion flat zone, and is suitable for high-resistance fault line selection of different grounding media.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flow chart of a method for selecting a high-resistance ground fault of a resonant ground power distribution network according to an embodiment of the present invention;
FIGS. 2 (a), (b) and (c) are respectively a half-wave waveform of zero-sequence current from minimum value to maximum value, a waveform of linearity of the half-wave of zero-sequence current with time window length change, and a change rate waveform of linearity with time window length change when line parameters are unbalanced in the embodiment of the present invention;
FIGS. 3 (a), (b) and (c) are respectively a half-wave waveform of zero-sequence current from maximum value to minimum value when line parameters are unbalanced, a waveform of linearity of the half-wave of the zero-sequence current with time window length change, and a change rate waveform of linearity with time window length change in the embodiment of the present invention;
FIGS. 4 (a), (b) and (c) are respectively a half-wave waveform of zero-sequence current of a fault line from a minimum value to a maximum value, a waveform of linearity of the half-wave of the zero-sequence current with time window length change, and a change rate waveform of linearity with time window length change in the high-resistance fault in the embodiment of the invention;
FIGS. 5 (a), (b) and (c) are respectively a half-wave waveform of zero-sequence current of a fault line from a maximum value to a minimum value, a waveform of linearity of the half-wave of the zero-sequence current with time window length change, and a change rate waveform of linearity with time window length change in the high-resistance fault in the embodiment of the invention;
FIGS. 6 (a), (b) and (c) are respectively a half-wave waveform of the zero-sequence current of the normal line from the minimum value to the maximum value, a waveform of the linearity of the half-wave of the zero-sequence current with the time window length change, and a change rate waveform of the linearity with the time window length change in the high-resistance fault in the embodiment of the invention;
fig. 7 (a), (b) and (c) are respectively a half-wave waveform of the zero-sequence current of the normal line from the maximum value to the minimum value, a waveform of the linearity of the half-wave of the zero-sequence current with the time window length change, and a change rate waveform of the linearity with the time window length change in the high-resistance fault in the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, based on the examples herein, which are within the scope of the invention as defined by the claims, will be within the scope of the invention as defined by the claims.
Example 1
As shown in fig. 1 and fig. 2, the present embodiment provides a method for selecting a high-resistance ground fault of a resonant ground distribution network, including:
step S1: and acquiring the zero sequence voltage of the bus of the power distribution network, and converting the zero sequence voltage of the bus to step S2 because the zero sequence voltage of the bus is larger than a zero sequence voltage setting value (5% of a rated value of phase voltage in the embodiment).
Step S2: acquiring a zero sequence current sequence { x (n) } of a feeder line on the bus; wherein the sequence { x (n) } of zero sequence currents is obtained by continuously sampling the zero sequence current of one feeder line on the bus for 0.03 seconds at a sampling frequency of 10kHz after a delay of 0.2 seconds, n=1, 2,3, …,300.
Step S3: acquiring a first local extreme point-minimum value point x (n) of a waveform of a zero-sequence zero-crossing point 1 ) Wherein n is 1 Is the sampling value sequence number of the extreme point; obtaining the second local extreme point of the waveform after zero-crossing again, namely the maximum point x (n) 2 ) Wherein n is 2 Is the sampling value sequence number of the extreme point; the zero sequence current waveform between the two extreme points is shown in fig. 2 (a). Wherein, for the first local extremum point and the second local extremum point, if the local extremum point is a maximum value, the value of the local extremum point is the maximum value of the continuous Z points with the local extremum point as the center; if the local extremum point is a minimum point, the value of the local extremum point is the minimum value of the consecutive Z points centered on the local extremum point, where the value of Z may be 7, 9 or 11, and in this embodiment, the value of Z is preferably 9.
Step S4: to be used forFor the center of the time window, let the width of the time window be 2w, wherein round is a rounding function, w is a positive integer smaller than 100/2 (equal to a sampling point in a half power frequency period), and the Linearity (Linearity) of the zero sequence current in the time window is obtained; the time window width is changed, and the zero sequence current linearity sequence L (w) under different time window widths is obtained, wherein w=1, 2,3, … and 49. The zero sequence current linearity sequence L (w) is calculated by the following method:
wherein,
step S5: and (3) adopting a 7-point linear fitting method to obtain a change rate (Gradient of Linearity) sequence GoL (k) of the zero sequence current linearity sequence, wherein k=1, 2,3, … and 44. The calculation formula of the change rate sequence GoL (k) is as follows:
wherein,the change rate of the curve is obtained by using 7 sampling points through a linear fitting method, the noise immunity is high, the random fluctuation of the change rate when signals are interfered by noise can be avoided, and the line selection accuracy is improved.
Step S6: as shown in fig. 2 (c), the sequence GoL (k) is almost all negative, and the number of positive values is less than 5 (5 is greater than 10% of 44), and it is determined that the line has no high-resistance ground fault (the three-phase parameters of the line may be unbalanced, or a low-resistance fault occurs, or other lines have high-resistance faults, but the line has no high-resistance ground fault).
Step S7: and (2) detecting other feeder lines on the bus by adopting the steps S2 to S6, and judging whether the feeder lines have single-phase high-resistance ground faults or not.
Example 2
As shown in fig. 1 and 3, this embodiment differs from embodiment 1 only in that:
step S3: obtaining the first local extreme point of the waveform after the zero-crossing of the zero-sequence current sequence for the first time, namely the maximum point x (n) 1 ) Wherein n is 1 Is the sampling value sequence number of the extreme point; acquiring a second local extreme point-minimum value point x (n) of the waveform after zero-crossing again of the zero-sequence current waveform 2 ) Wherein n is 2 Is the sampling value sequence number of the extreme point; the zero sequence current waveform between the two extreme points is shown in fig. 3 (a).
Step S6: as shown in fig. 3 (c), the sequence GoL (k) is almost positive and the number of negative values is less than 5, and it is determined that the line has no high-resistance ground fault (the three-phase parameters of the line may be unbalanced, or a low-resistance fault occurs, or other lines have high-resistance faults, but the line has no high-resistance ground fault).
Example 3
As shown in fig. 1 and 4, this embodiment differs from embodiment 1 only in that:
step S3: acquiring a first local extreme point-minimum value point x (n) of a waveform of a zero-sequence zero-crossing point 1 ) Wherein n is 1 Is the sampling value sequence number of the extreme point; obtaining the second local extreme point of the waveform after zero-crossing again, namely the maximum point x (n) 2 ) Wherein n is 2 Is the sampling value sequence number of the extreme point; the zero sequence current waveform between the two extreme points is shown in fig. 4 (a).
Step S6: as shown in fig. 4 (c), the sequence GoL (k) has a positive number and a negative number which are approximately equal and are all much larger than 5, and it is determined that the high-resistance ground fault occurs in the line.
Example 4
As shown in fig. 1 and 5, this embodiment differs from embodiment 1 only in that:
step S3: obtaining the first local extreme point of the waveform after the zero-crossing of the zero-sequence current sequence for the first time, namely the maximum point x (n) 1 ) Wherein n is 1 Is the sampling value sequence number of the extreme point; acquiring a second local extreme point-minimum value point x (n) of the waveform after zero-crossing again of the zero-sequence current waveform 2 ) Wherein n is 2 Is the sampling value sequence number of the extreme point; the zero sequence current waveform between the two extreme points is shown as 5 (a).
Step S6: as shown in fig. 5 (c), the sequence GoL (k) has a positive number and a negative number which are approximately equal and are all much larger than 5, and it is determined that the high-resistance ground fault occurs in the line.
Example 5
As shown in fig. 1 and 6, this embodiment differs from embodiment 1 only in that:
step S3: acquiring the first zero-crossing waveform of the zero-sequence currentLocal extreme point-minimum point x (n 1 ) Wherein n is 1 Is the sampling value sequence number of the extreme point; obtaining the second local extreme point of the waveform after zero-crossing again, namely the maximum point x (n) 2 ) Wherein n is 2 Is the sampling value sequence number of the extreme point; the zero sequence current waveform between the two extreme points is shown in fig. 6 (a).
Step S6: as shown in fig. 6 (c), the sequence GoL (k) is all negative, the number of positive is 0, and the number of positive is less than 5 (5 is greater than 10% of 44), and it is determined that the line has no high-resistance ground fault (the three-phase parameters of the line may be unbalanced, or a low-resistance fault occurs, or other lines have high-resistance faults, but the line has no high-resistance ground fault).
Example 6
As shown in fig. 1 and 7, this embodiment differs from embodiment 1 only in that:
step S3: obtaining the first local extreme point of the waveform after the zero-crossing of the zero-sequence current sequence for the first time, namely the maximum point x (n) 1 ) Wherein n is 1 Is the sampling value sequence number of the extreme point; acquiring a second local extreme point-minimum value point x (n) of the waveform after zero-crossing again of the zero-sequence current waveform 2 ) Wherein n is 2 Is the sampling value sequence number of the extreme point; the zero sequence current waveform between the two extreme points is shown in fig. 7 (a).
Step S6: as shown in fig. 7 (c), the sequence GoL (k) is positive, the number of negative values is 0, and is less than 5 (5 is greater than 10% of 44), and it is determined that the line has no high-resistance ground fault (the three-phase parameters of the line may be unbalanced, or a low-resistance fault occurs, or other lines have high-resistance faults, but the line has no high-resistance ground fault).
Example 7
The embodiment provides a high-resistance ground fault line selection system, which comprises:
the primary judgment module is used for acquiring the zero sequence voltage of the bus of the power distribution network, judging that the power distribution network is suspected of single-phase earth fault if the zero sequence voltage of the bus is larger than a zero sequence voltage setting value, and repeating the judgment process if the power distribution network is not suspected of single-phase earth fault;
the fault detection module is used for respectively detecting high-resistance grounding faults of each feeder line on the bus and judging whether single-phase high-resistance grounding faults occur or not; the fault detection module comprises a sampling unit, a linearity acquisition unit, a change rate acquisition unit and a fault judgment unit; wherein:
the sampling unit is used for acquiring a zero sequence current sequence { x (n) } of one feeder line on the bus; the zero sequence current sequence { x (N) } is obtained by continuously sampling zero sequence current of one feeder line on a bus for a preset time length at a preset sampling frequency, wherein n=1, 2,3, …, and N are the total number of samples;
the linearity obtaining unit is used for obtaining a first local extreme point x (n) of the waveform after the zero-crossing of the zero-sequence current sequence for the first time 1 ) Wherein n is 1 Is the sampling value sequence number of the extreme point; acquiring a second local extreme point x (n) of the waveform after zero-sequence current waveform crosses zero again 2 ) Wherein n is 2 Is the sampling value sequence number of the extreme point; to be used forFor the center of the time window, the width of the time window is 2w, wherein round is a rounding function, w is a positive integer smaller than M, and the linearity of the zero sequence current in the time window is obtained; changing the time window width, and obtaining zero sequence current linearity sequences L (w) under different time window widths, wherein w=1, 2,3, …, M-1 and M are preset values;
the change rate acquisition unit is used for solving a change rate sequence GoL (k) of the zero sequence current linearity sequence;
the fault judging unit is used for judging that the feeder line has high-resistance ground fault when the numbers of positive and negative in the change rate sequence GoL (k) are not smaller than the preset number; otherwise, the feeder line does not have a high resistance ground fault.
Other specific implementation procedures in this embodiment can be seen in the foregoing embodiments 1 to 6, and will not be described herein.
Example 8
The present embodiment provides a computer-readable storage medium storing a computer program adapted to be loaded by a processor and to perform the high-resistance ground fault line selection method according to any one of embodiments 1 to 6.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
It is to be understood that the same or similar parts in the above embodiments may be referred to each other, and that in some embodiments, the same or similar parts in other embodiments may be referred to.
Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps of the process, and further implementations are included within the scope of the preferred embodiment of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present invention.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.
Claims (8)
1. The high-resistance ground fault line selection method for the resonant grounding power distribution network is characterized by comprising the following steps of:
step S1: acquiring the zero sequence voltage of a bus of the power distribution network, if the zero sequence voltage of the bus is larger than the zero sequence voltage setting value, turning to step S2, otherwise, repeating step S1;
step S2: acquiring a zero sequence current sequence { x (n) } of a feeder line on the bus; the zero sequence current sequence { x (N) } is obtained by continuously sampling zero sequence current of one feeder line on a bus for a preset time length at a preset sampling frequency, wherein n=1, 2,3, …, and N are the total number of samples;
step S3: acquiring a first local extreme point x (n) of a waveform after the zero-crossing of the zero-sequence current sequence 1 ) Wherein n is 1 Is the sampling value sequence number of the extreme point; acquiring a second local extreme point x (n) of the waveform after zero-sequence current waveform crosses zero again 2 ) Wherein n is 2 Is the sampling value sequence number of the extreme point;
step S4: to be used forFor the center of the time window, the width of the time window is 2w, wherein round is a rounding function, w is a positive integer smaller than M, and the linearity of the zero sequence current in the time window is obtained; changing the time window width, and obtaining zero sequence current linearity sequences L (w) under different time window widths, wherein w=1, 2,3, …, M-1 and M are preset values;
step S5: the change rate sequence GoL (k) of the zero sequence current linearity sequence is obtained;
step S6: if the numbers of positive and negative values in the change rate sequence GoL (k) are not smaller than the preset number, judging that the feeder line has high-resistance ground faults; otherwise, the feeder line does not have high-resistance ground fault;
step S7: S2-S6 are adopted to detect other feeder lines on the bus, and whether single-phase high-resistance ground faults occur or not is judged;
the zero sequence current linearity sequence L (w) in the step S4 is obtained by calculation through the following method:
wherein,
in the step S5, a 7-point linear fitting method is adopted to calculate a change rate sequence GoL (k) of the zero sequence current linearity sequence, and the calculation formula is as follows:
wherein,
2. the method for selecting a high-resistance ground fault line for a resonant ground power distribution network according to claim 1, wherein the zero sequence voltage setting value in step S1 is 5% of the nominal value of the phase-taking voltage.
3. The method for selecting a high-impedance ground fault line for a resonant ground power distribution network according to claim 1, wherein the delay time is at least 0.2 seconds before the sampling in step S2.
4. The method for selecting a high-impedance ground fault line for a resonant ground power distribution network according to claim 1, wherein the preset sampling frequency in the step S2 is 10kHz, and the preset duration is not shorter than 0.03 seconds.
5. The method according to claim 1, wherein for the first local extremum point and the second local extremum point in the step S3, if the local extremum point is the maximum value, the value of the local extremum point is the maximum value of the continuous Z points centered on the local extremum point; if the local extremum point is a minimum point, the value of the local extremum point is the minimum value of the continuous Z points centered on the local extremum point, wherein Z takes on a value of 7, 9 or 11.
6. The method for selecting a high-resistance ground fault line of a resonant ground power distribution network according to claim 1, wherein the value of M in the step S4 is 50, and the preset number in the step S6 is 5.
7. A resonant ground distribution network high-resistance ground fault line selection system, comprising:
the primary judging module is used for acquiring the zero sequence voltage of the bus of the power distribution network, and judging that the power distribution network is suspected of single-phase earth fault if the zero sequence voltage of the bus is greater than a zero sequence voltage setting value;
the fault detection module is used for respectively detecting high-resistance grounding faults of each feeder line on the bus and judging whether single-phase high-resistance grounding faults occur or not; the fault detection module comprises a sampling unit, a linearity acquisition unit, a change rate acquisition unit and a fault judgment unit; wherein:
the sampling unit is used for acquiring a zero sequence current sequence { x (n) } of one feeder line on the bus; the zero sequence current sequence { x (N) } is obtained by continuously sampling zero sequence current of one feeder line on a bus for a preset time length at a preset sampling frequency, wherein n=1, 2,3, …, and N are the total number of samples;
the linearity obtaining unit is used for obtaining a first local extreme point x (n) of the waveform after the zero-crossing of the zero-sequence current sequence for the first time 1 ) Wherein n is 1 Is the sampling value sequence number of the extreme point; acquiring a second local extreme point x (n) of the waveform after zero-sequence current waveform crosses zero again 2 ) Wherein n is 2 Is the sampling value sequence number of the extreme point; to be used forFor the center of the time window, the width of the time window is 2w, wherein round is a rounding function, w is a positive integer smaller than M, and the linearity of the zero sequence current in the time window is obtained; changing the time window width, and obtaining zero sequence current linearity sequences L (w) under different time window widths, wherein w=1, 2,3, …, M-1 and M are preset values;
the change rate acquisition unit is used for solving a change rate sequence GoL (k) of the zero sequence current linearity sequence;
the fault judging unit is used for judging that the feeder line has high-resistance ground fault when the numbers of positive and negative in the change rate sequence GoL (k) are not smaller than the preset number; otherwise, the feeder line does not have high-resistance ground fault;
the zero sequence current linearity sequence L (w) is calculated by the following method:
wherein,
the change rate sequence GoL (k) of the zero sequence current linearity sequence is calculated by adopting a 7-point linear fitting method, and the calculation formula is as follows:
wherein,
8. a computer readable storage medium storing a computer program adapted to be loaded by a processor and to perform a resonant ground power distribution network high resistance ground fault line selection method according to any one of claims 1 to 6.
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