CN113419136A - Method and system for detecting fault moment of power distribution network - Google Patents
Method and system for detecting fault moment of power distribution network Download PDFInfo
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Abstract
The invention provides a method and a system for detecting a power distribution network fault moment, wherein the method comprises the following steps: acquiring a phase current signal in real time; applying current break variable fault detection to the current signal to obtain a fault occurrence time prejudgment point; generating a data window according to the prejudgment point; and performing multi-stage morphological gradient operation on the current data in the data window, and determining the fault occurrence time according to the extreme point of the operation result. The invention improves the multi-stage morphological gradient algorithm on the basis of the traditional mutation detection algorithm, is less influenced by data disturbance, has high algorithm reliability, can accurately identify the mutation position of a current signal, and is not influenced by attenuated direct current components and the occurrence time of faults.
Description
Technical Field
The invention relates to the technical field of power distribution network protection and control, in particular to a method and a system for detecting a fault moment of a power distribution network.
Background
In the application of relay protection, the method has very important significance for accurately detecting the fault moment, and particularly for a power distribution network with generally low sampling rate. Taking the differential protection which takes the fault time as the synchronous reference in the distribution network as an example, the reliability of the differential protection is closely related to the accurate fault occurrence time.
With the wide access of the distributed power supply, the network structure of the power distribution network is changed from a traditional radial network into a network of double-end or even multi-end power supplies, and the access of the distributed power supply changes the fault characteristics of the system. In this case, in order to improve the power supply reliability of the power distribution network, the differential protection principle is introduced into the power distribution network and is applied to a certain extent. The differential protection based on the fault time self-synchronization principle is provided by being limited by the communication level and the information transmission capability in the power distribution network and combining the characteristics of the power distribution network, and the two-end protection carries out subsequent sampling and calculates corresponding electric quantity by taking the respective detected fault occurrence time as a time reference. The method makes the two-side protection relatively independent in time, does not need real-time setting, and reduces the requirement on a communication path, but the method inevitably generates synchronization errors caused by different moments of the two-side protection detection faults. The traditional fault moment detection adopts a phase current sudden change quantity detection principle, the synchronization error generated by the principle is influenced by factors such as the fault occurrence moment, the fault characteristics of the distributed power supply, the starting threshold value and the like, the situation of a large value can occur under extreme conditions, and once the synchronization error exceeds the allowable margin of the synchronization error, the protection can be rejected when the fault occurs in a region. Therefore, in order to reduce the error generated by the self-synchronization principle of the fault time and to make the differential protection widely used in the distribution network, the fault occurrence time must be accurately detected.
Aiming at the problem of detection errors in phase current mutation detection, the existing fault moment detection method comprises wavelet transformation, singular value decomposition, current mutation curve fitting and the like. However, these methods have the disadvantages of high sampling frequency requirement, long sampling data window, complex operation, poor anti-interference performance and the like.
Disclosure of Invention
The invention provides a method and a system for detecting a power distribution network fault moment, which are used for solving the problems of high sampling frequency requirement and complex operation of the existing fault moment detection method.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a method for detecting a fault moment of a power distribution network, which comprises the following steps:
acquiring a phase current signal in real time;
applying current break variable fault detection to the current signal to obtain a fault occurrence time prejudgment point;
generating a data window according to the prejudgment point;
and performing multi-stage morphological gradient operation on the current data in the data window, and determining the fault occurrence time according to the extreme point of the operation result.
Further, the specific process of performing multistage morphological gradient operation on the current data in the data window and determining the fault occurrence time according to the extreme point of the operation result is as follows:
performing multi-stage morphological gradient operation on the current data in the data window to obtain an output result of the gradient operation;
determining sampling points corresponding to a first extreme point and a second extreme point of the gradient operation result;
the mean value of the two sampling points is the fault occurrence time.
Further, searching an extreme point from a fourth point of an output result of the gradient operation, and selecting the first two extreme points as the first extreme point and the second extreme point, wherein the absolute value of the extreme point is greater than 0.1. I2N，I2NIs the secondary rating of the current transformer.
Further, the mean value of the two sampling points is rounded up to an adjacent integer as the fault occurrence time.
Further, the specific process of detecting the current mutation amount to obtain the pre-judgment point at the fault occurrence time is as follows:
the fault detection of the phase current abrupt change is carried out by adopting the following formula
Wherein i represents a current instantaneous value, Δ i represents a current abrupt change amount,
for phase, m represents discrete sampling points, N is the number of sampling points per cycle, IsetIs a set threshold value;
and taking the first point of the three continuous points as a prejudgment point.
Furthermore, the data window is formed by selecting sampling point data of a half cycle before the pre-judging point and a quarter cycle after the pre-judging point.
Further, the multistage morphological gradient operation formula is as follows:
in the formula (I), the compound is shown in the specification,
theta is respectivelyThe dilation and erosion operators, n is the sampling point,
Gγrespectively representing the result of the gradient of the rising edge, the result of the gradient of the falling edge and the result of the gradient of the whole signal, G0As current sample values in the data window, g+、g-The structural elements that highlight the rising and falling edges of the signal, respectively.
Further, the value of gamma is 3, the structural element is a slope structural element, and the length is 2.
The invention provides a system for detecting the fault moment of a power distribution network, which comprises:
the information acquisition unit is used for acquiring phase current signals in real time;
the first processing unit is used for applying current mutation fault detection to the current signal to obtain a fault occurrence time prejudgment point;
the second processing unit generates a data window according to the pre-judging point;
and the detection unit is used for performing multi-stage morphological gradient operation on the current data in the data window and determining the fault occurrence time according to the extreme point of the operation result.
A third aspect of the invention provides a computer storage medium having stored thereon computer instructions which, when run on the detection system, cause the detection system to perform the detection method as described.
The system for detecting a power distribution network fault time according to the second aspect of the present invention can implement the methods according to the first aspect and the implementation manners of the first aspect, and achieve the same effects.
The effect provided in the summary of the invention is only the effect of the embodiment, not all the effects of the invention, and one of the above technical solutions has the following advantages or beneficial effects:
1. the invention improves the multi-stage morphological gradient algorithm on the basis of the traditional mutation detection algorithm, is less influenced by data disturbance, has high algorithm reliability, can accurately identify the mutation position of a current signal, and is not influenced by attenuated direct current components and the occurrence time of faults.
2. The invention considers the influence of the morphological endpoint effect, needs 3/4 cycle data windows, only 1/4 cycle data after the fault, and when the sampling rate is high, the data window can be shortened to half cycle. Besides, the morphology only comprises addition and subtraction and the operation of taking the most value, other complicated operation processes are not involved, and only a very small calculation amount needs to be added on the basis of the mutation amount detection method.
3. The invention has low requirement on the phase current sampling rate, can still ensure the detection error smaller than one sampling interval at 1.6kHz, can still be suitable under the condition of lower sampling rate of a power distribution network, and has better application situation.
4. The detection errors of the invention are all smaller than a sampling interval and have no large fluctuation, and the synchronization error generated in the application taking the fault moment as the data synchronization reference is almost 0, thereby laying a foundation for the application of the invention in the power distribution network.
Drawings
In order to more clearly illustrate the embodiments or technical solutions in the prior art of the present invention, the drawings used in the description of the embodiments or prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.
FIG. 1 is a schematic flow diagram of an embodiment of the method of the present invention;
FIG. 2 is a schematic diagram of an active power distribution network system in accordance with an embodiment of the method of the present invention;
FIG. 3 is a schematic diagram of the A-phase current measured by the system side protection of the faulty line and the processing result of the method according to the present invention when a fault occurs at a certain time in the embodiment of the present invention;
FIG. 4 is a schematic diagram of the A-phase current measured by the system side protection of the faulty line and the processing result of the method according to the present invention when the fault occurs at another time in the embodiment of the present invention;
fig. 5 shows a measured a-phase current of the protection on the distributed power supply side of the fault line at another time of the fault according to the embodiment of the present invention and the processing result of the method according to the present invention.
Detailed Description
In order to clearly explain the technical features of the present invention, the following detailed description of the present invention is provided with reference to the accompanying drawings. The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. It should be noted that the components illustrated in the figures are not necessarily drawn to scale. Descriptions of well-known components and processing techniques and procedures are omitted so as to not unnecessarily limit the invention.
As shown in fig. 1, the method for detecting a power distribution network fault time provided by the present invention includes the following steps:
acquiring a phase current signal in real time; the current signal is obtained by acquiring the value of the current transformer in real time through the protection device.
When the phase current sudden change fault detection condition is met, applying current sudden change fault detection to the current signal to obtain a fault occurrence time prejudgment point, and setting the prejudgment point as the kth point0And (4) sampling points.
The fault detection principle of phase current break variable adopts the following formula
Wherein i represents a current instantaneous value, Δ i represents a current abrupt change amount,
for phase, m represents the mth discrete sampling point, N is the number of sampling points per cycle, IsetIs a set threshold value. I isset＝K·I2N，I2NAnd K is a proportionality coefficient which is a secondary rated value of the current transformer and is usually 0.3.
k0Taken as the first of three consecutive points that satisfy the above equation.
Generating a data window according to the prejudgment point; considering the detection error possibly existing in the mutation quantity principle and the end point effect of morphology, the data window is selected as follows: k is a radical of0Half cycle before point and k0The data of the sampling points one quarter cycle after the point form a data window.
Performing multi-stage morphological gradient operation on the current data in the data window to obtain an output result of the gradient operation; the multi-stage morphological gradient operation formula applied by the invention is as follows:
in the formula (I), the compound is shown in the specification,
Θ is the basic morphological dilation and erosion operators, respectively, and n represents the nth sample point in the discrete data.
Gγ(γ ═ 0,1,2, 3.) denotes the leading edge gradient result, the trailing edge gradient result, and the gradient result of the entire signal, respectively, when the γ -order gradient calculation is performed, G0As current sample values in the data window, g+、g-Are the structural elements that highlight the rising and falling edges of the signal, respectively. The multi-stage morphological gradient operation applied by the invention improves the traditional algorithm, and all levels of morphological gradient operation are takenThe same structural elements.
g+＝M·{1,0}、g-＝M·{ 0 And 1, all are slope structural elements with the length of 2, the underline position is the origin of the structural element, and M is the amplitude of the slope structural element.
M＝20·I2N，I2NIs the secondary rating of the current transformer.
In this embodiment, a 3-stage modified morphological gradient operation is performed, i.e., γ is 3, and the length of the structural element is always 2.
Determining sampling points corresponding to a first extreme point and a second extreme point of the gradient operation result; searching for extreme points from the fourth point of the output result of the 3-level morphological gradient operation, and taking the first two extreme points, wherein the absolute value of the extreme points is required to be more than 0.1 & I2N。
The mean value of the two sampling points is the fault occurrence time. The mean value is rounded up to the nearest integer, with the point representing the time of occurrence of the fault, on the basis of which the subsequent related application can be made with the time of the fault as the reference for synchronization. The result of removing the influence of the end-point effect is recorded as valid data, and the above-mentioned determination of the data window, k0The quarter cycle sampling point is taken after the point to eliminate the end effect influence, and actually only k is taken0Four points after the point are sufficient.
The process of the present invention is further illustrated by the following specific examples.
As shown in fig. 2, in this example, the power grid system is a 10kV active power distribution network including Distributed Generators (DG), which are all inversion-type DG, the system frequency is 50Hz, and the secondary rated current of the current transformer is 5A.
In the example, the sampling frequency is firstly set to be 4kHz, and the M, N side protection device collects phase current signals of the current transformer in real time;
0.50125s, a three-phase grounding short-circuit fault occurs at point f in FIG. 2, and the transition resistance is 5 Ω;
at this time, the fault currents on the two sides of M, N meet the fault detection criterion of the phase current abrupt change quantity:
wherein i represents a current instantaneous value, Δ i represents a current abrupt change amount,
the other is. N is the number of sampling points per cycle, IsetFor the set threshold value, N is 80 in this example, Iset＝1.5A。
Determining k0Point, k in this example040 points before the point and k 020 sampling points after the point form a data window;
and performing improved multistage morphological gradient operation on the current data in the data window:
in the formula (I), the compound is shown in the specification,
theta is the basic morphological dilation and erosion operator, respectively
And (3) expansion operation:
and (3) corrosion operation:
in the formula: f (n) is an input signal, and the domain is DfG (m) is a structural function and the definition domain is Dg. 3-stage improved form gradient operation (IMMG3) is carried out on the current sampling values in the data window in the example to obtain an output result G3. In this example, the gradient structural element, g+＝100·{1,0}、g-＝100·{01, all levels of gradient operation adopt the structural element, and the underline position is the origin of the structural element.
Determining a gradient operation result G3The sampling points corresponding to the first extreme point and the second extreme point are respectively Kfir、Ksec；
Get Kfir、KsecThe mean value of the two is recorded as the signal discontinuity point, rounded up to the nearest integer, and recorded as the detected fault occurrence time kf。
Fig. 3 shows the a-phase current measured by the M-side protection and the algorithm processing result in this embodiment. The algorithm detection result is as follows: first extreme point KfirCorresponding time Tfir0.501s, second extreme point KsecCorresponding time is TsecWhen the failure occurrence time is obtained as 0.50125s, 0.5015s is identical to the actual failure occurrence time, and in this case, there is no detection error.
In this example, at 0.50611s, a two-phase short-circuit fault occurs at point f in fig. 2, the transition resistance is still 5 Ω, fig. 4 shows the a-phase current and the algorithm processing result measured by the M-side protection in this embodiment, and fig. 5 shows the a-phase current and the algorithm processing result measured by the N-side protection in this embodiment. As shown in fig. 4 and 5, the phase current sudden change principle detects the fault occurrence time k0The results were: m side, 0.50625s, detection error 2.52 °; on the N side, 0.51s, the detection error is 70.02 °, and the synchronization error generated on both sides is 67.5 °. The detection results of the algorithm of the invention on M, N side current are as follows: when the fault occurs for 0.506s, the detection error is-1.98 degrees, and the synchronization error generated on the two sides is 0.
In this example, the sampling frequency was changed to 1.6kHz, 32 points were sampled per cycle, and the rest was the same as when the sampling frequency was 4kHz, 0.50125sA two-phase short circuit fault occurs via a 5 omega transition resistance. The detection results of the algorithm on the currents on the two sides M, N are as follows: first extreme point KfirCorresponding time Tfir0.495s, second extreme point KsecCorresponding time is TsecWhen the failure occurrence time is obtained as 0.50125s, 0.5075s is identical to the actual failure occurrence time, and in this case, there is no detection error.
In this example, after the sampling frequency is changed, a two-phase short-circuit fault occurs at point f in fig. 2 at 0.50611s, the transition resistance is still 5 Ω, and the detection result of the algorithm for the current on the M side is: the fault occurrence time is 0.50625s, the detection error is 2.52 degrees, and the detection result of the algorithm on the N-side current is as follows: the time of occurrence of the fault is 0.505625s, the detection error is-8.73 degrees, the generated synchronization error is 11.25 degrees, and the generated synchronization error is just the angle interval of the next sampling point at the sampling rate. When the mutation measurement algorithm is used for detection, the fault time detected by the M side is 0.506875s, the detection error is 13.77 degrees, the fault time detected by the N side is 0.510625s, the detection error is 81.27 degrees, and the detection error is far larger than the result obtained by the algorithm.
The invention also provides a detection system for the power distribution network fault moment, which comprises an information acquisition unit, a first processing unit, a second processing unit and a detection unit.
The information acquisition unit is used for acquiring phase current signals in real time; the first processing unit applies current mutation fault detection to the current signal to obtain a fault occurrence time prejudgment point; the second processing unit generates a data window according to the pre-judging point; the detection unit performs multi-stage morphological gradient operation on the current data in the data window, and determines the fault occurrence time according to the extreme point of the operation result.
The invention also provides a computer storage medium, wherein computer instructions are stored in the computer storage medium, and when the computer instructions are operated on the detection system, the detection system is enabled to execute the detection method.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.
Claims (10)
1. A method for detecting a power distribution network fault moment is characterized by comprising the following steps:
acquiring a phase current signal in real time;
applying current break variable fault detection to the current signal to obtain a fault occurrence time prejudgment point;
generating a data window according to the prejudgment point;
and performing multi-stage morphological gradient operation on the current data in the data window, and determining the fault occurrence time according to the extreme point of the operation result.
2. The method for detecting the power distribution network fault moment according to claim 1, wherein the specific process of performing multistage morphological gradient operation on the current data in the data window and determining the fault occurrence moment according to the extreme point of the operation result comprises the following steps:
performing multi-stage morphological gradient operation on the current data in the data window to obtain an output result of the gradient operation;
determining sampling points corresponding to a first extreme point and a second extreme point of the gradient operation result;
the mean value of the two sampling points is the fault occurrence time.
3. The method according to claim 2, wherein the first two extreme points are selected as the first extreme point and the second extreme point, starting from the fourth point of the output result of the gradient operation, and the absolute value of the extreme points is greater than 0.1-l2N，I2NIs the secondary rating of the current transformer.
4. The method for detecting the fault time of the power distribution network according to claim 2, wherein the mean value of the two sampling points is rounded up to an adjacent integer as the fault occurrence time.
5. The method for detecting the power distribution network fault moment according to claim 1 or 2, wherein the specific process of detecting the current mutation amount and obtaining the fault occurrence moment prejudgment point is as follows:
the fault detection of the phase current abrupt change is carried out by adopting the following formula
Wherein i represents a current instantaneous value, Δ i represents a current abrupt change amount,
for phase, m represents discrete sampling points, N is the number of sampling points per cycle, IsetIs a set threshold value;
and taking the first point of the three continuous points as a prejudgment point.
6. The method for detecting the power distribution network fault moment according to claim 1 or 2, wherein the data window is formed by selecting sampling point data of a half cycle before a pre-judgment point and a quarter cycle after the pre-judgment point.
7. The method for detecting the fault moment of the power distribution network according to claim 1 or 2, wherein the multistage morphological gradient operation formula is as follows:
in the formula (I), the compound is shown in the specification,
theta is the expansion and corrosion operators, respectively, n is the sampling point,
Gγrespectively representing the result of the gradient of the rising edge, the result of the gradient of the falling edge and the result of the gradient of the whole signal, G0As current sample values in the data window, g+、g-The structural elements that highlight the rising and falling edges of the signal, respectively.
8. The method for detecting the power distribution network fault moment as claimed in claim 7, wherein the value of gamma is 3, the structural elements are slope structural elements, and the length of the slope structural elements is 2.
9. A system for detecting the fault moment of a power distribution network is characterized by comprising:
the information acquisition unit is used for acquiring phase current signals in real time;
the first processing unit is used for applying current mutation fault detection to the current signal to obtain a fault occurrence time prejudgment point;
the second processing unit generates a data window according to the pre-judging point;
and the detection unit is used for performing multi-stage morphological gradient operation on the current data in the data window and determining the fault occurrence time according to the extreme point of the operation result.
10. A computer storage medium having computer instructions stored thereon, which when run on the inspection system of claim 9, cause the inspection system to perform the inspection method of claim 1 or 2.
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