A Pilot Protection Method for Distribution Networks Based on the Weighted Minkowski Distance Method

Abstract

The present invention discloses a pilot protection method for active distribution networks based on weighted Minkowski distance, belonging to the field of relay protection in power systems. Two sets of relay protection devices with the same parameters are installed at the head and end of the distribution network line respectively. The protection on each side independently measures the current sampling values on its own side, obtains the current data on the opposite side at the same moment through the communication device, and calculates the weighted Minkowski distance M<subgt;1< / subgt> between the current data in a one-cycle sampling time window on both sides, the weighted Minkowski distance M<subgt;2< / subgt> of the positive sequence components of the three-phase current, and the weighted Minkowski distance M<subgt;3< / subgt> of the negative sequence components. If M<subgt;r is less than its corresponding operating threshold, there is no internal fault and the protection does not operate, where r = 1, 2, 3; for any M<subgt;r exceeding its corresponding operating threshold, the circuit breaker performs a tripping operation. This method can be applied to active distribution networks with different penetration rates and different types of new energy access, with wide adaptability and good reliability.

Description

Technical Field

[0001] The present invention relates to the field of relay protection of power systems, and particularly to a pilot protection method based on the weighted Minkowski distance method. Background Art

[0002] In order to cope with global climate change, new energy power generation represented by wind energy and solar energy has developed rapidly. However, in the case of a large number of new energy grid connections, the distribution network has a complex topological structure and two-way power flow, and the grid fault characteristics show limited current amplitude, frequency deviation, and non-fundamental frequency harmonics.

[0003] The invention application CN112491019A, an intelligent analysis method for the action of relay protection in a distribution network, collects and analyzes the data information on which the relay protection in the distribution network acts from an information platform; determines the type of in-station protection action; judges whether each type of in-station protection action is correct. If so, the relay protection in the distribution substation operates normally without any treatment; otherwise, the relay protection in the distribution network operates abnormally, stores the protection information of the abnormal operation of the relay protection in the distribution network in a database, and generates an analysis report on the abnormal operation of the protection action; and pushes the analysis report on the abnormal operation of the protection action to the staff, improving the work efficiency of the staff, facilitating the staff to master the true situation of the distribution network fault, and ensuring the processing speed of the abnormal situation of the distribution network. However, the data collection and processing methods are not designed in detail and cannot directly solve the specific technical problems of the grid fault.

[0004] At present, there are great differences between the grid fault characteristics and those of the traditional synchronous power grid, posing a severe challenge to the traditional three-stage relay protection based on synchronous generators. Therefore, it is of great significance to propose a new relay protection scheme under the background of a large increase in the proportion of new energy power generation. Summary of the Invention

[0005] The purpose of the present invention is to provide a pilot protection method for a distribution network based on the weighted Minkowski distance method, which has the advantages of high reliability and wide adaptability, and is applicable to the fault protection of active distribution networks under different penetration rates.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A pilot protection method for a distribution network based on the weighted Minkowski distance, the method comprising:

[0008] Step 1: Sampling the current data within the set sampling time window at both the head end M and the tail end N of the line respectively, and obtaining the current data within the same cycle and the same sampling time window on both sides through a communication device;

[0009] Step 2: Take the Minkowski distance parameter p as p = 1, 2, 3 respectively, and calculate the distance between the current data of the same cycle sampling time window on both sides. The Minkowski distance of the positive sequence component of the three-phase current and the Minkowski distance of the negative sequence component

[0010] Step 3: Perform a weighted operation on to obtain the weighted Minkowski distance M r , where M1 represents the Minkowski distance between the current data of one cycle sampling time window after weighting, M2 represents the Minkowski distance of the positive sequence component of the three-phase current of one cycle sampling time window after weighting, M3 represents the Minkowski distance of the negative sequence component of the three-phase current of one cycle sampling time window after weighting, and r = 1, 2, 3;

[0011] Step 4: If 0 ≤ M r ≤ ε r , then there is no internal fault in the line and the protection does not operate; for any M r exceeding its corresponding action threshold, that is, M r >ε r , then trip the circuit breaker to cut off the fault, where ε r is the action threshold of M r , and r = 1, 2, 3. ε r is set according to the empirical value or the debugging value.

[0012] Furthermore, the calculation method of the is as follows:

[0013]

[0014] where the point set i M ={i M1 , i M2 , i M3 …i Mn} is the current sampling value at the head of the line at different times; the point set i N ={i N1 , i N2 , i N3 …i Nn} is the current sampling value at the end of the line at different times, and p = 1, 2, 3.

[0015] The calculation method of the is as follows:

[0016]

[0017] where the point set is the positive sequence component of the current sampling values at the head of the line at different times; the point set is the positive sequence component of the current sampling values at the end of the line at different times, where p = 1, 2, 3.

[0018] The is calculated as follows:

[0019]

[0020] Among them, the point set is the negative sequence component of the current sampling values at the head of the line at different times; the point set is the negative sequence component of the current sampling values at the end of the line at different times, where p = 1, 2, 3.

[0021] Furthermore, the length of the sampling time window is set to 20 ms.

[0022] Furthermore, the sampling frequency is 1.2 kHz.

[0023] Furthermore, the weighted operation is as follows:

[0024]

[0025] Among them, n is the number of current transformer samplings, and w p is the weighting coefficient when p takes different values; p = 1, 2, 3; r = 1, 2, 3, represents the distance between the current data of the sampling time window of one cycle on both sides of the line, represents the Minkowski distance of the positive sequence component of the three-phase current, represents the Minkowski distance of the negative sequence component.

[0026] Furthermore, two sets of relay protection devices with the same parameters are installed on both sides of the head M and the end N of the line, and the protection on each side independently measures the current sampling values on its own side.

[0027] Beneficial effects

[0028] 1. A pilot protection method for a distribution network based on the weighted Minkowski distance method according to the present invention realizes accurate fault judgment by calculating the Euclidean distance of the currents at the head and end of the line at the same moment, effectively making up for the problems of difficult fault judgment and removal of active distribution networks by traditional relay protection devices under different penetration rates and different types of new energy access, and has good reliability.

[0029] 2. The present invention is oriented to the power grid environment of new energy power generation represented by wind energy and solar energy, has the advantages of wide application range, etc., and conforms to the trend of the development of the contemporary power industry. Description of the drawings

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 A flow chart of a distribution network longitudinal protection method based on the weighted Minkowski distance method provided in an embodiment of the invention;

[0032] Figure 2 This is a schematic diagram of the active distribution network topology and faults within the area in the example of the present invention;

[0033] Figure 3 This is a schematic diagram of an active distribution network relay protection device in an example of the present invention. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. The described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Various modifications and improvements made to the technical solutions of the present invention by ordinary persons in this field without departing from the design concept of the present invention should fall within the scope of protection of the present invention.

[0035] Distance metric is based on the distance between two vectors and is mainly used to describe the similarity between two sets of points. Suppose there are two sets of points in space:

[0036] A={a1,a2,a3,…,a p},B={b1,b2,b3,…,b p}

[0037] Then the Minkowski distance between two sets of points is:

[0038]

[0039] Here, the two point sets A and B represent the sampling data of the current transformer, and n is the number of sampling points.

[0040] The closer the distance between the two sets of vectors, the smaller the resulting Minkowski distance. Furthermore, the Minkowski distance essentially calculates and identifies faults based on current amplitude, encompassing both fundamental and harmonic component information. Compared to traditional relay protection devices, it offers superior selectivity, adapting to the increasing access of new energy sources to distribution networks and effectively resolving the difficulty of extracting fault features.

[0041] The following is an introduction to the working conditions of relay protection devices in distribution networks under different operating conditions:

[0042] 1. Normal operation

[0043] The current characteristics at the beginning of the line are obtained using a 20ms time window sampling. The current characteristics at the end of the line are obtained using a 20ms data window sampling. Current sampling data from the opposite side is obtained through communication devices at both ends of the line. The weighted Minkowski distance M1 of each phase current, as well as the weighted Minkowski distances M2 and M3 of the positive and negative sequence components of the three-phase currents, are calculated between the current data from the same sampling time window on both sides over one cycle. Thus, the following is true:

[0044] 0≤M r ≤ε r

[0045] where ε r is the action threshold, r=1,2,3. r If the value is less than the action threshold, the protection will not take effect.

[0046] 2. Faults within the area

[0047] like Figure 2 As shown, an internal fault occurs in the distribution network. The current characteristics of the line head end are obtained by sampling with a time window width of 20ms at the line head end, and the current characteristics of the line head end are obtained by sampling with a data window width of 20ms at the line head end. Then, the current information of the opposite side is obtained through the communication equipment, and the weighted Minkowski distance M1 of each phase current and the weighted Minkowski distances M2 and M3 of the positive and negative sequence components of the three-phase current are calculated between the current data of the same sampling time window in one cycle on both sides. For the weighted Minkowski distance M1 between the current data of the same sampling time window in one cycle at both ends of the line, the weighted Minkowski distance M2 of the positive sequence component of the current and the weighted Minkowski distance M3 of the negative sequence component, as long as any one of them exceeds its corresponding action threshold, the circuit breaker will perform a tripping operation, that is, So that:

[0048] M r >ε r

[0049] The following is a detailed description of the process of the above method with a specific example. Figure 2 The figure shows the simulation model of the active power distribution network in the example of the present invention. Figure 2Shown in the figure is an active distribution network with a voltage level of 10 kV. The transformer adopts the Dyn connection method, and the transformation ratio is 110 kV / 10 kV; the line is set with the following parameters: the protection area is line EF, with a length of 5 km. The positive and negative sequence impedances of the line are both Z1 = 0.076 + j0.338 Ω / km, and the zero sequence impedance is Z0 = 0.386 + j0.824 Ω / km. A distributed photovoltaic power plant with a capacity of 1.5 MW is connected to the end of line FG. Load L A has an active power of 1 MW and a reactive power of 0.8 MVar; Load L B has an active power of 2 MW and a reactive power of 0.6 Mvar; L C has an active power of 1 MW and a reactive power of 0.8 MVar.

[0050] There are 6 fault locations in total, including 4 in-zone faults, which are respectively set at 0.5 km, 1.5 km, 3.75 km, and 4.5 km from the beginning of line EF, accounting for 15%, 30%, 75%, and 90% of the line length respectively, and are respectively marked as K1, K2, K3, and K4; 2 out-of-zone faults are respectively in line NE and line FG, and are respectively marked as K5 and K6. The fault types include single-phase grounding fault, two-phase grounding fault, two-phase short-circuit fault, and three-phase short-circuit fault. Taking phase A grounding, AB two-phase grounding, BC two-phase fault, and ABC three-phase short-circuit as examples, they are respectively denoted as AG, ABG, BC, and ABC. The faults are set at 0.1 s after the simulation starts, the sampling frequency is 1.2 kHz, and the number of sampling points is 24. When p = 1, w1 takes When p = 2, w2 takes When p = 3, w3 takes When the protection action threshold of the Minkowski coefficient is set by avoiding the weighted Minkowski distance of the protected line during normal operation and out-of-zone faults, in this example, the action threshold value of the weighted Minkowski distance of the three-phase current is set to 8, the action threshold value of the weighted Minkowski distance of the positive sequence component of the three-phase current is set to 1, and the action threshold value of the weighted Minkowski distance of the negative sequence component of the current is set to 0.5.

[0051] As Figure 3 shown is the schematic connection diagram of the line relay protection device of the active distribution network in the example of the present invention. As Figure 3 shown, relay protection devices 1 and 2 are respectively installed at the beginning and end of the line. The two devices independently measure the three-phase current information on their own sides. After sampling, the current information on their own sides is sent to the opposite side through the communication channel. Then, the two devices calculate the Euclidean distance between the currents at the beginning and end of the line and the weighted Minkowski distance of the positive and negative sequence components of the three-phase current at the beginning and end of the line in the same cycle and the same time window. If the weighted Minkowski distance exceeds the action threshold, a tripping signal is sent to the corresponding circuit breaker.

[0052] To further verify the effectiveness of the method proposed by the present invention, simulations were carried out in the simulation software Simulink for different positions and different fault types in Figure 2 . Table 1 gives the weighted Minkowski distances of the phase currents under different fault positions and fault types, and Table 2 gives the weighted Minkowski distances of the positive and negative sequence components of the three-phase currents under different fault positions and fault types.

[0053] The data in Table 1 and Table 2 show that the method proposed by the present invention can accurately and reliably identify in-zone and out-of-zone faults in active distribution networks, effectively making up for the problems of traditional relay protection devices in judging and removing faults in active distribution networks under different penetration rates and different types of new energy access.

[0054] Table 1

[0055]

[0056]

[0057] Table 2

[0058]

[0059] As described above, it is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A pilot protection method for distribution networks based on the weighted Minkowski distance method, characterized in that, The method includes: Step 1: Current data sampling is completed on both sides of the line head M and the line end N respectively within a set sampling time window, and the current data within the same cycle and the same sampling time window on both sides is obtained through a communication device; Step 2: Let the Minkowski distance parameter \(p\) take values of \(p = 1, 2, 3\) respectively, and calculate the distances between the current data of one - cycle sampling time windows on both sides of the same line The Minkowski distance of the positive - sequence components of the three - phase current and the Minkowski distance of the negative - sequence components The said is calculated as follows: Among them, the point set \(i\) M =\(\{i\) M1 , i M2 , i M3 … \(i\) Mn \} is the current sampling value at the head of the line at different times; the point set \(i\) N =\(\{i\) N1 , i N2 , i N3 … \(i\) Nn \} is the current sampling value at the end of the line at different times, where \(p = 1, 2, 3\). The calculation method is as follows: Among them, the point set is the positive-sequence component of the current sampling values at the line head at different times; the point set is the positive-sequence component of the current sampling values at the line end at different times, where p = 1, 2, 3; The calculation method is as follows: Among them, the point set is the negative sequence component of the current sampling values at the line head at different times; the point set is the negative sequence component of the current sampling values at the line end at different times, where p = 1, 2, 3; Step 3. Perform weighted operation on to obtain the weighted Minkowski distance M r , where r = 1, 2, 3; the weighted operation is as follows: where n is the number of samples of the current transformer, and w p is the weighting coefficient when p takes different values. M1 represents the Minkowski distance between the current data of a weighted one-cycle sampling time window, M2 represents the Minkowski distance of the positive-sequence components of the three-phase current in a weighted one-cycle sampling time window, M3 represents the Minkowski distance of the negative-sequence components of the three-phase current in a weighted one-cycle sampling time window, and r = 1, 2, 3; Step 4: If 0 ≤ M r ≤ ε r , there is no internal fault in the line and the protection does not operate; for any M r exceeding its corresponding operating threshold, that is, M r > ε r , the circuit breaker is tripped to cut off the fault, where ε r is the operating threshold of M r .

2. The pilot protection method for distribution network based on the weighted Minkowski distance method according to claim 1, characterized in that The length of the sampling time window is set to 20 ms.

3. The pilot protection method for distribution network based on the weighted Minkowski distance method according to claim 2, wherein The sampling frequency is 1.2 kHz.

4. The pilot protection method for distribution network based on the weighted Minkowski distance method according to claim 1, wherein Two sets of relay protection devices with the same parameters are installed on both sides of the line head M and the line end N respectively to independently measure the current data on this side.

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