Fault upstream and downstream judgment method based on instantaneous symmetric component method

Abstract

The invention discloses a fault upstream and downstream judgment method based on an instantaneous symmetric component method. The fault upstream and downstream judgment method comprises the following steps: S1, monitoring current data of each node of a power distribution network in real time; s2, calculating an instantaneous positive sequence current and an instantaneous negative sequence current of the real-time data by adopting an improved instantaneous symmetric component method; s3, performing primary difference on the instantaneous positive-sequence current and the instantaneous negative-sequence current respectively; s4, comparing the primary differential value of the instantaneous negative-sequence current with a set threshold value, and judging whether the directions of the instantaneous positive-sequence current and the instantaneous negative-sequence current are the same or not; and S5, performing fault section judgment by combining the direction of the instantaneous positive and negative sequence current and the topological structure of the power distribution network. The improved instantaneous symmetric component method is used to obtain the instantaneous positive-sequence current and the instantaneous negative-sequence current, the directions of the instantaneous positive-sequence current and the instantaneous negative-sequence current are analyzed, the fault section can be quickly and accurately positioned, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network fault location, and in particular to a method for determining upstream and downstream faults based on an instantaneous symmetrical component method. Background Art

[0002] The distribution network has the characteristics of complex network structure, many branch lines, large number of equipment and wide distribution. It is easily affected by various factors, which may lead to failure of the distribution network. Once a failure occurs, if the fault point cannot be located in time and accurately, the power outage time will be prolonged, which will bring great inconvenience to users and may also cause huge economic losses.

[0003] At present, the fault location of distribution network often adopts the traveling wave positioning technology, which is to install the traveling wave detection device at the specific location of the distribution network, measure the arrival time of the traveling wave signal, and calculate the location of the fault point according to the speed and time difference of the traveling wave propagation. However, the traveling wave positioning technology requires the installation of more traveling wave detection devices in the distribution network, which is costly; the propagation of traveling wave signals is affected by line parameters, environmental factors, etc., which may cause errors in the positioning results.

[0004] You can also use big data and artificial intelligence positioning data to analyze and mine a large amount of historical fault data and real-time monitoring data in the distribution network, use artificial intelligence algorithms to establish a fault diagnosis model, and realize the positioning and prediction of distribution network faults. However, big data and artificial intelligence algorithms require a large amount of historical data and high-performance computing equipment, and the cost of data collection, storage and processing is high; the training and optimization of artificial intelligence algorithms require professional technicians and a long time. Or use intelligent algorithm positioning technology, such as genetic algorithms or ant colony algorithms. However, intelligent algorithm positioning technology has problems such as large computational complexity and premature convergence, which may lead to slow positioning speed and long search time when the network structure is complex. Summary of the invention

[0005] In order to solve the problems of inaccurate positioning, long positioning time and high cost in the existing distribution network fault positioning methods, the present invention proposes a fault upstream and downstream judgment method based on the instantaneous symmetrical component method. According to the real-time monitored voltage and current data, the improved instantaneous symmetrical component method is used to calculate the instantaneous positive sequence current and the instantaneous negative sequence current of each node. By analyzing the directions of the two, the fault section can be quickly and accurately positioned to solve the above problems.

[0006] The present application discloses a method for determining upstream and downstream faults based on an instantaneous symmetrical component method, comprising the following steps:

[0007] S1. Real-time monitoring of current data at each node of the distribution network, including substations;

[0008] S2, using the improved instantaneous symmetrical component method, calculates the instantaneous positive sequence current and instantaneous negative sequence current of the real-time data obtained in S1;

[0009] S3, perform a differential on the instantaneous positive sequence current and the instantaneous negative sequence current respectively;

[0010] S4, comparing the primary differential value of the instantaneous negative sequence current with the set threshold value, if it exceeds the set threshold value, determining whether the directions of the instantaneous positive and negative sequence currents are the same;

[0011] S5. The fault section is determined based on the directions of the instantaneous positive and negative sequence currents and the topological structure of the distribution network.

[0012] Preferably, the calculation formulas for the instantaneous positive sequence current and the instantaneous negative sequence current are as follows:

[0013]

[0014] Among them, i a(1) is the instantaneous positive sequence current of phase A at the current moment, i b(1) is the instantaneous positive sequence current of phase B at the current moment, i c(1) is the instantaneous positive sequence current of phase C at the current moment, i a(2) is the instantaneous negative sequence current of phase A at the current moment, i b(2) is the instantaneous negative sequence current of phase B at the current moment, i c(2) is the instantaneous negative sequence current of phase C at the current moment, is the rotating phasor of phase A, is the B phase rotation vector, is the C-phase rotating phasor, and Im represents the imaginary part.

[0015] Preferably, the difference calculation formula of S3 is as follows:

[0016]

[0017]

[0018] Among them, i a(1) (t-△t) is the instantaneous positive sequence current of phase A at the previous moment, i a(2) (t-△t) is the instantaneous negative sequence current of phase A at the previous moment, D (1) is the direction of the instantaneous positive sequence current, D (2) is the direction of the instantaneous negative sequence current.

[0019] Preferably, the direction of the instantaneous positive and negative sequence current is determined by the following formula:

[0020] Judge (Direction) =D (1) ·D (2) ;

[0021] Preferably, the method for determining the direction of the instantaneous positive and negative sequence current is:

[0022] If Judge (Direction) >0, the directions of instantaneous positive and negative sequence currents are the same;

[0023] If Judge (Direction) <0, the directions of the instantaneous positive and negative sequence currents are opposite.

[0024] Preferably, the fault section determination method is:

[0025] Assume CT1 and CT2 are two points in the distribution network, and CT1 is located upstream of CT2;

[0026] If the instantaneous positive and negative sequence currents at CT2 are opposite, that is, Judge (Direction) CT2<0, and the instantaneous positive and negative sequence currents at CT1 have the same direction, that is, Judge (Direction) When CT2>0, it can be determined that the fault point is between CT1 and CT2.

[0027] Beneficial effects of the present invention:

[0028] (1) Accurate positioning, able to accurately determine the section where the fault occurs.

[0029] (2) Fast positioning speed: when the current transformer rate is 1 kHz, the fault section can be located within 0.08 seconds.

[0030] (3) Low cost: the fault section can be quickly identified by utilizing the current monitoring devices at existing substations and other nodes.

[0031] (3) Power supply reliability is enhanced, and the faulty section can be quickly identified and accurately removed, greatly reducing the risk of power outages. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of a method for determining upstream and downstream faults based on an instantaneous symmetrical component method according to an embodiment of the present invention;

[0033] Figure 2 The figure is a schematic diagram of the fault point location principle according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples.

[0035] The embodiment of the present invention discloses a method for judging upstream and downstream faults based on the instantaneous symmetrical component method, the process is as follows: Figure 1 As shown, the following steps are included:

[0036] S1. Real-time monitoring of current data at each node of the distribution network, including substations.

[0037] S2. Use the improved instantaneous symmetrical component method to calculate the instantaneous positive sequence current and instantaneous negative sequence current of the real-time data obtained in S1.

[0038] Since the traditional instantaneous symmetric vector method has a certain delay in calculation, which affects the real-time performance of the symmetric component transformation, this embodiment adopts an improved instantaneous symmetric vector method to obtain the instantaneous values ​​of the positive-sequence, negative-sequence, and zero-sequence components of the three-phase electricity in real time by constructing a rotating vector.

[0039] For the instantaneous value of three-phase unbalanced current:

[0040]

[0041] Among them, i a 、i b 、i c are the instantaneous values ​​of the three-phase currents, I am ,I bm ,I cm are the amplitudes of the three-phase currents, φ a ,φ b ,φ c are the initial phases of the three-phase currents, ω is the angular frequency, and t is the time.

[0042] Assume that the corresponding rotating phasors are:

[0043]

[0044] in, They are three-phase rotating phasors respectively.

[0045] The instantaneous current of phase A can be expressed as:

[0046] i a (t) = I am sin[ω(t-△t+△t)+φ a ]

[0047] =I am sin[ω(t-△t)+φ a ]cos(ω△t)+I am cos[ω(t-△t)+φ a ]sin(ω△t);

[0048] Among them, i a (t) is the instantaneous current of phase A, and △t is the time interval.

[0049] Right now:

[0050] i a (t) = i a (t-△t)cos(ω△t)+I am cos[ω(t-△t)+φ a ]sin(ω△t);

[0051] From this we can get:

[0052]

[0053] And because:

[0054] I am cos(ωt+φ a )

[0055] =I am cos[ω(t-△t+△t)+φ a ]cos(ω△t)-I am sin[ω(t-△t)+φ a ]sin(ω△t);

[0056] Then we can get:

[0057] I am cos(ωt+φ a )=[i a (t)-i a (t-△t)cos(ω△t)]·cot(ω△t)-i a (t-△t)sin(ω△t);

[0058] Similarly, we can get:

[0059]

[0060]

[0061] Among them, i b (t) is the instantaneous current of phase B, i c (t) is the instantaneous current of phase C.

[0062] The known steady-state symmetric component method is:

[0063]

[0064] in, is the positive sequence current of phase A obtained using the symmetrical component method, is the negative sequence current of phase A obtained using the symmetrical component method, is the zero-sequence current of phase A obtained using the symmetrical component method. a is the rotation factor, which means that the vector rotates 120° counterclockwise.

[0065] After sorting, the instantaneous values ​​of the positive and negative sequence components of the three-phase current can be obtained:

[0066]

[0067]

[0068] Among them, i a(1) is the instantaneous positive sequence current of phase A at the current moment, i b(1) is the instantaneous positive sequence current of phase B at the current moment, i c(1) is the instantaneous positive sequence current of phase C at the current moment, i a(2) is the instantaneous negative sequence current of phase A at the current moment, i b(2) is the instantaneous negative sequence current of phase B at the current moment, i c(2) is the instantaneous negative sequence current of phase C at the current moment, and Im represents the imaginary part.

[0069] S3. Perform a differential on the instantaneous positive sequence current and the instantaneous negative sequence current respectively.

[0070] After obtaining the instantaneous positive and negative sequence current sequence through S2, the direction of the instantaneous positive and negative sequence current can be determined by sequentially differentiating.

[0071] The difference calculation formula is as follows:

[0072]

[0073] Among them, i a(1) (t-△t) is the instantaneous positive sequence current of phase A at the previous moment, i a(2) (t-△t) is the instantaneous negative sequence current of phase A at the previous moment, D (1) is the direction of the instantaneous positive sequence current, D (2) is the direction of the instantaneous negative sequence current.

[0074] S4. Compare the instantaneous negative sequence current primary difference value with the set threshold value. In this embodiment, the set threshold value is 0. If it exceeds the set threshold value, determine whether the directions of the instantaneous positive and negative sequence currents are the same. The direction of the instantaneous positive and negative sequence currents is determined by the following formula:

[0075] Judge (Direction) =D (1) ·D (2) ;

[0076] The method for determining the direction of instantaneous positive and negative sequence current is:

[0077] If Judge (Direction) >0, the directions of instantaneous positive and negative sequence currents are the same;

[0078] If Judge(Direction) <0, the directions of the instantaneous positive and negative sequence currents are opposite.

[0079] S5. The fault section is determined based on the directions of the instantaneous positive and negative sequence currents and the topological structure of the distribution network.

[0080] Assume that CT1 and CT2 are two points in the distribution network, and CT1 is located upstream of CT2. In a specific embodiment, Figure 2 As shown in the figure, when an asymmetric fault occurs at the position shown in the figure, if the instantaneous positive and negative sequence currents at CT2 are opposite, that is, Judge (Direction) CT2<0, and the instantaneous positive and negative sequence currents at CT1 have the same direction, that is, Judge (Direction) When CT2>0, it can be determined that the fault point is between CT1 and CT2.

[0081] This application uses the improved instantaneous symmetrical component method to calculate the instantaneous positive sequence current and instantaneous negative sequence current of each node based on the voltage and current data monitored in real time at the substation and other key nodes. By analyzing the direction of the two, it is possible to quickly and accurately locate the fault section. During the implementation process, the current monitoring devices of the existing substations and other nodes are fully utilized to quickly determine the fault section. This not only opens up a new idea for the new protection setting of relay protection equipment and effectively saves costs, but also has important significance for accurately removing faults in a short time. This move can significantly improve the reliability of power supply in the distribution network, avoid large-scale power outages caused by faults, and has outstanding engineering application value.

[0082] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for judging upstream and downstream faults based on the instantaneous symmetrical component method, characterized in that: The following steps are involved: S1. Real-time monitoring of current data at each node of the distribution network, including substations; S2, using the improved instantaneous symmetrical component method, calculates the instantaneous positive sequence current and instantaneous negative sequence current of the real-time data obtained in S1; S3, perform a differential on the instantaneous positive sequence current and the instantaneous negative sequence current respectively; S4, comparing the primary differential value of the instantaneous negative sequence current with the set threshold value, if it exceeds the set threshold value, determining whether the directions of the instantaneous positive and negative sequence currents are the same; S5. The fault section is determined based on the directions of the instantaneous positive and negative sequence currents and the topological structure of the distribution network.

2. The method for determining upstream and downstream faults based on the instantaneous symmetrical component method according to claim 1, characterized in that: The calculation formulas for the instantaneous positive sequence current and the instantaneous negative sequence current are as follows: Among them, i a(1) is the instantaneous positive sequence current of phase A at the current moment, i b(1) is the instantaneous positive sequence current of phase B at the current moment, i c(1) is the instantaneous positive sequence current of phase C at the current moment, i a(2) is the instantaneous negative sequence current of phase A at the current moment, i b(2) is the instantaneous negative sequence current of phase B at the current moment, i c(2) is the instantaneous negative sequence current of phase C at the current moment, is the rotating phasor of phase A, is the B phase rotation vector, is the C-phase rotating phasor, and Im represents the imaginary part.

3. The method for determining upstream and downstream faults based on the instantaneous symmetrical component method according to claim 2 is characterized in that: The differential calculation formula of S3 is as follows: Among them, i a(1) (t-△t) is the instantaneous positive sequence current of phase A at the previous moment, i a(2) (t-△t) is the instantaneous negative sequence current of phase A at the previous moment, D (1) is the direction of the instantaneous positive sequence current, D (2) is the direction of the instantaneous negative sequence current.

4. The method for determining upstream and downstream faults based on the instantaneous symmetrical component method according to claim 3 is characterized in that: The determination of the direction of the instantaneous positive and negative sequence current is completed by the following formula: Judge (Direction) =D (1) ·D (2) ; Among them, D (1) is the direction of the instantaneous positive sequence current, D (2) is the direction of the instantaneous negative sequence current.

5. The method for determining upstream and downstream faults based on the instantaneous symmetrical component method according to claim 4 is characterized in that: The method for determining the direction of the instantaneous positive and negative sequence current is: If Judge (Direction) >0, the directions of instantaneous positive and negative sequence currents are the same; If Judge (Direction) <0, the directions of the instantaneous positive and negative sequence currents are opposite.

6. The method for determining upstream and downstream faults based on the instantaneous symmetrical component method according to claim 5, characterized in that: The fault section determination method is as follows: Assume CT1 and CT2 are two points in the distribution network, and CT1 is located upstream of CT2; If the instantaneous positive and negative sequence currents at CT2 are opposite, that is, Judged (Direction) CT2<0, and the instantaneous positive and negative sequence currents at CT1 have the same direction, that is, Judge (Direction) When CT2>0, it can be determined that the fault point is between CT1 and CT2.

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