Medium-voltage distribution network / medium-voltage micro-grid multi-terminal pilot protection method, system and equipment

Abstract

The invention discloses a medium-voltage power distribution network / medium-voltage micro-grid multi-terminal pilot protection method, system and device, and the method comprises the steps: obtaining a three-phase current fault component and a three-phase voltage at each switch of a T-connection multi-terminal line protection region of a medium-voltage power distribution network / medium-voltage micro-grid within a time window; wherein the switches comprise a first switch on a transformer substation side and second switches which are correspondingly connected with the loads respectively; the modulus of the three-phase current fault component and the modulus of the three-phase voltage of each switch are obtained, and then the cosine similarity coefficient of each switch is obtained; obtaining a cosine similarity coefficient product of the first switch and each second switch, and further obtaining a cosine similarity coefficient product sum; and when the product sum of the cosine similarity coefficients is smaller than or equal to the protection setting value, judging that a fault occurs in the region, performing pilot protection action, and tripping a switch in the region. According to the invention, accurate judgment of a fault section and accurate and rapid fault isolation can be realized while reducing the level difference of communication channel performance requirements, and the power supply reliability is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power system relay protection, and particularly relates to a multi-terminal longitudinal protection method, system and device for a medium-voltage distribution network / medium-voltage microgrid. BACKGROUND

[0002] As a core link of the terminal power system, the medium-voltage distribution network and the medium-voltage microgrid based on the construction of the medium-voltage distribution network are directly connected to users, and are of great significance to guarantee power supply and meet user demand. The medium-voltage distribution network / medium-voltage microgrid protection undertakes the heavy task of removing faults and guaranteeing the safety of equipment and power supply reliability, and it is of great significance to design it with high performance.

[0003] However, the traditional over-current protection for the medium-voltage distribution network / medium-voltage microgrid based on single-end data has low selectivity, and the field generally realizes hierarchical protection through the differential coordination between the over-current protections of the upstream and downstream lines. However, the medium-voltage distribution network / medium-voltage microgrid line is relatively long, and the number of line switches is as high as 4 or more. Moreover, due to the long tripping time of the medium-voltage distribution network / medium-voltage microgrid line switch, only two-stage hierarchical protection of "substation feeder line protection + boundary line protection" or three-stage hierarchical protection of "substation feeder line protection + branch line protection + boundary line protection" can be realized, and it is difficult to realize the reasonable differential coordination of the key path switches of the medium-voltage distribution network / medium-voltage microgrid line. The fault of the main line where the sectional switch is located will cause the over-current protection of the substation feeder line to act, that is, the whole line will be powered off.

[0004] Moreover, the tripping of the traditional over-current protection can only realize the tripping of the switch upstream of the fault point. If the power supply of the non-fault section is to be restored, the downstream switch of the fault point must be manually tripped for fault isolation, and then the tie switch must be closed for power supply restoration. The time for the power supply of the non-fault section to be restored is long, which greatly affects the power supply reliability. Therefore, it is necessary to introduce longitudinal protection with high selectivity into the medium-voltage distribution network / medium-voltage microgrid to realize accurate judgment and precise and rapid isolation of the fault section, provide a basis for rapid power restoration of the non-fault section, and thus improve the power supply reliability.

[0005] There is a longitudinal differential protection method based on real-time current differential principle in the existing protection field of the medium-voltage distribution network / medium-voltage microgrid. However, in order to solve the construction cost, the medium-voltage distribution network / microgrid generally adopts T-connected lines for construction. In this case, longitudinal differential protection for 3-terminal lines to more than 10-terminal lines in some areas is required. The high sampling rate real-time analog data required for differential transmission will result in a large amount of transmission data, which requires high performance of the communication channel. This obviously does not meet the economic requirements of the construction of the medium-voltage distribution network / medium-voltage microgrid.

[0006] Therefore, after the line fault of the medium-voltage distribution network / medium-voltage micro-grid, the traditional overcurrent protection has low selectivity, low power supply capacity, and the current differential protection has large data transmission volume and high requirements for communication channels in the multi-terminal system, which needs to be improved, and the case is generated accordingly. SUMMARY

[0007] The purpose of the present application is to provide a medium-voltage distribution network / medium-voltage micro-grid multi-terminal longitudinal protection method, system and device, which can accurately determine the fault section and quickly isolate the fault with reduced performance requirements for communication channels, and improve the power supply reliability.

[0008] In order to achieve the above purpose, the solution of the present application is:

[0009] A medium-voltage distribution network / medium-voltage micro-grid multi-terminal longitudinal protection method, comprising,

[0010] Obtaining three-phase current fault components and three-phase voltages at each switch in a medium-voltage distribution network / medium-voltage micro-grid T-connected multi-terminal line protection area within a time window; wherein the switches include a first switch at a substation and a second switch connected to each load respectively;

[0011] According to the three-phase current fault components and the three-phase voltages, the modulus of the three-phase current fault components and the modulus of the three-phase voltages at each switch are obtained;

[0012] According to the modulus of the three-phase current fault components and the modulus of the three-phase voltages at each switch, the cosine similarity coefficients of each switch are obtained;

[0013] According to the cosine similarity coefficients of each switch, the cosine similarity coefficient products of the first switch and each second switch are obtained, and then the cosine similarity coefficient product sum is obtained;

[0014] The cosine similarity coefficient product sum is compared with the protection setting value, and when the cosine similarity coefficient product sum is less than or equal to the protection setting value, it is judged that a fault occurs in the medium-voltage distribution network / medium-voltage micro-grid T-connected multi-terminal line protection area, and the cascade protection acts to trip the switches in the area.

[0015] Wherein, obtaining three-phase current fault components at each switch in a medium-voltage distribution network / medium-voltage micro-grid T-connected multi-terminal line protection area within a time window comprises,

[0016] Obtaining a fault starting time;

[0017] Obtaining three-phase currents at each switch in a medium-voltage distribution network / medium-voltage micro-grid T-connected multi-terminal line protection area within a time window from the fault starting time;

[0018] According to the three-phase currents, the three-phase current fault components at each switch are obtained.

[0019] wherein, the three-phase voltage at each switch in the T-connected multi-terminal line protection area of the medium-voltage distribution network / medium-voltage micro-grid in a time window is obtained, including,

[0020] the fault starting time is obtained;

[0021] the three-phase voltage at each switch in the T-connected multi-terminal line protection area of the medium-voltage distribution network / medium-voltage micro-grid in a time window starting from a set time before the fault starting time is obtained.

[0022] wherein, the fault starting time is obtained, including,

[0023] the three-phase current at each switch is obtained;

[0024] the three-phase current at each switch is compared with the overcurrent element judgment constant value, and the three-phase current at at least one switch is greater than the overcurrent element judgment constant value, and the current time is the fault starting time.

[0025] wherein, the overcurrent element judgment constant value is set as the maximum load current of the medium-voltage distribution network / medium-voltage micro-grid line.

[0026] wherein, the modulus of the three-phase current fault component at each switch is obtained according to the three-phase current fault component and the three-phase voltage, including,

[0027] the Clark phase module transformation is performed according to the three-phase current fault component Δi Ak , Δi Bk , Δi Ck of a certain switch k,

[0028]

[0029] the modulus of the three-phase current fault component at the switch k is obtained as Δi k ;

[0030] wherein, the modulus of the three-phase voltage at each switch is obtained according to the three-phase current fault component and the three-phase voltage, including,

[0031] the Clark phase module transformation is performed according to the three-phase voltage u Ak , u Bk , u Ck of a certain switch k,

[0032]

[0033] the modulus of the three-phase voltage at the switch k is obtained as u k .

[0034] wherein, the cosine similarity coefficient of each switch is obtained according to the modulus of the three-phase current fault component and the modulus of the three-phase voltage at each switch, including,

[0035] According to the modulus Δi of the three-phase current fault component of a certain switch k i and the modulus u of the three-phase voltage i , the following operation is performed,

[0036]

[0037] to obtain the cosine similarity coefficient cosθ of the switch k k ; wherein j=1, 2…N, N represents the total number of sampling points in the time window.

[0038] A medium-voltage distribution network / medium-voltage micro-grid multi-terminal longitudinal protection system, comprising,

[0039] a three-phase current fault component and three-phase voltage acquisition module configured to acquire three-phase current fault components and three-phase voltages at each switch in a medium-voltage distribution network / medium-voltage micro-grid T-connected multi-terminal line protection area within a time window; wherein the switches include a first switch at a substation and second switches respectively connected corresponding to each load;

[0040] a modulus acquisition module configured to obtain the modulus of the three-phase current fault component and the modulus of the three-phase voltage of each switch according to the three-phase current fault component and the three-phase voltage;

[0041] a cosine similarity coefficient acquisition module configured to obtain the cosine similarity coefficient of each switch according to the modulus of the three-phase current fault component and the modulus of the three-phase voltage of each switch;

[0042] a cosine similarity coefficient product sum acquisition module configured to obtain the cosine similarity coefficient product of the first switch and each second switch according to the cosine similarity coefficient of each switch, and further obtain the cosine similarity coefficient product sum; and

[0043] a fault judgment and processing module configured to compare the cosine similarity coefficient product sum with a protection setting value, and when the cosine similarity coefficient product sum is less than or equal to the protection setting value, judge that a fault occurs in the medium-voltage distribution network / medium-voltage micro-grid T-connected multi-terminal line protection area, and the longitudinal protection acts to trip the switches in the area.

[0044] wherein the three-phase current fault component and three-phase voltage acquisition module acquires three-phase current fault components at each switch in a medium-voltage distribution network / medium-voltage micro-grid T-connected multi-terminal line protection area within a time window, comprising,

[0045] acquiring a fault starting time;

[0046] acquiring three-phase currents at each switch in a medium-voltage distribution network / medium-voltage micro-grid T-connected multi-terminal line protection area within a time window starting from the fault starting time;

[0047] According to the three-phase current, three-phase current fault components at each switch are obtained.

[0048] The three-phase voltage obtaining module obtains three-phase voltages at each switch in the protection area of the T-connected multi-terminal line of the medium-voltage distribution network / medium-voltage micro-grid in a time window, including,

[0049] The fault starting moment is obtained.

[0050] The three-phase voltages at each switch in the protection area of the T-connected multi-terminal line of the medium-voltage distribution network / medium-voltage micro-grid in a time window are obtained since a set time length before the fault starting moment.

[0051] The fault starting moment is obtained, including,

[0052] The three-phase current at each switch is obtained.

[0053] The three-phase current at each switch is compared with an overcurrent element judgment constant value, and if the three-phase current at at least one switch is greater than the overcurrent element judgment constant value, the current time is the fault starting moment.

[0054] The overcurrent element judgment constant value is set as the maximum load current of the medium-voltage distribution network / medium-voltage micro-grid line.

[0055] The module obtaining module obtains the modulus of the three-phase current fault components at each switch according to the three-phase current fault components and the three-phase voltages, including,

[0056] According to the three-phase current fault components Δi Ak , Δi Bk , and Δi Ck of a certain switch k, Clark phase modulus transformation is performed,

[0057]

[0058] The modulus of the three-phase current fault components at the switch k is obtained as Δi k .

[0059] The module obtaining module obtains the modulus of the three-phase voltages at each switch according to the three-phase current fault components and the three-phase voltages, including,

[0060] According to the three-phase voltages u Ak , u Bk , and u Ck of a certain switch k, Clark phase modulus transformation is performed,

[0061]

[0062] The modulus of the three-phase voltages at the switch k is obtained as uk .

[0063] wherein, the cosine similarity coefficient acquisition module obtains the cosine similarity coefficient of each switch according to the modulus of the three-phase current fault component and the modulus of the three-phase voltage of each switch, including,

[0064] According to the modulus of the three-phase current fault component of a certain switch k i and the modulus of the three-phase voltage u i , the following operation is performed,

[0065]

[0066] The cosine similarity coefficient cosθ k of the switch k is obtained; wherein, j=1, 2…N, N represents the total number of sampling points in the time window.

[0067] A computer device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor; the processor implements the steps of the medium voltage distribution network / medium voltage micro-grid multi-terminal pilot protection method as described above when executing the computer program.

[0068] A computer readable storage medium stores a computer program; the computer program is executed by a processor to implement the steps of the medium voltage distribution network / medium voltage micro-grid multi-terminal pilot protection method as described above.

[0069] After the above scheme is adopted, compared with the prior art, the application utilizes the characteristics that there is a huge difference between the current fault component at the switch measurement point of the medium voltage distribution network / medium voltage micro-grid line and the voltage polarity before the fault at the #1 switch, introduces a cosine similarity coefficient to measure the difference, and constructs a protection criterion based on the cosine similarity product sum. The protection method proposed in the application can realize accurate judgment of the fault section and precise and rapid isolation of the fault, improve the power supply reliability, and only needs to communicate the calculation results of the cosine similarity coefficients after the fault is started between the protection terminals of each switch, that is, without the real-time transmission of a large amount of high-frequency collected analog quantity data, avoiding the problem of large data transmission rate, and having engineering implementation feasibility of the application of the medium voltage distribution network / medium voltage micro-grid T-connected multi-terminal line. BRIEF DESCRIPTION OF DRAWINGS

[0070] Figure 1 is a flowchart of the method of the application;

[0071] Figure 2 is a system structure diagram of the medium voltage distribution network / medium voltage micro-grid system with a T-connected line according to the application;

[0072] Figure 3is the power distribution network system structure diagram of the present application only containing T connection line of #1, #2, #3 switches;

[0073] Figure 4 is the fault current polarity of each switch when the fault occurs in the area of the present application;

[0074] Figure 5 is the fault current polarity of each switch when the fault occurs outside the area of the present application;

[0075] Figure 6 is the line mode component of fault current of #1, #2, #3 switches and the line mode component of voltage before the fault when the fault occurs in the area of the present application;

[0076] Wherein, (a) is the line mode component of voltage before the fault in the area, (b) is the line mode component of fault current of #1 switch when the fault occurs in the area, (c) is the line mode component of fault current of #2 switch when the fault occurs in the area, (d) is the line mode component of fault current of #3 switch when the fault occurs in the area;

[0077] Figure 7 is the cosine similarity coefficient of #1, #2, #3 switches when the fault occurs in the area of the present application;

[0078] Wherein, (a) is the cosine similarity coefficient of #1 switch when the fault occurs in the area, (b) is the cosine similarity coefficient of #2 switch when the fault occurs in the area, (c) is the cosine similarity coefficient of #3 switch when the fault occurs in the area;

[0079] Figure 8 is the line mode component of fault current of #1, #2, #3 switches and the line mode component of voltage before the fault when the fault occurs outside the area of the present application;

[0080] Wherein, (a) is the line mode component of voltage before the fault outside the area, (b) is the line mode component of fault current of #1 switch when the fault occurs outside the area, (c) is the line mode component of fault current of #2 switch when the fault occurs outside the area, (d) is the line mode component of fault current of #3 switch when the fault occurs outside the area;

[0081] Figure 9 is the cosine similarity coefficient of #1, #2, #3 switches when the fault occurs outside the area of the present application;

[0082] Wherein, (a) is the cosine similarity coefficient of #1 switch when the fault occurs outside the area, (b) is the cosine similarity coefficient of #2 switch when the fault occurs outside the area, (c) is the cosine similarity coefficient of #3 switch when the fault occurs outside the area. DETAILED DESCRIPTION

[0083] The present application provides a kind of medium voltage distribution network / medium voltage microgrid multi-terminal longitudinal protection method, comprising,

[0084] The three-phase current fault components and three-phase voltages at each switch in the T-connected multi-terminal line protection area of ​​the medium-voltage distribution network / medium-voltage microgrid within a certain time window are obtained; wherein, the switch includes a first switch on the substation side and a second switch connected to each load respectively;

[0085] Based on the three-phase current fault components and three-phase voltages, the modulus of the three-phase current fault components and the modulus of the three-phase voltages of each switch are obtained.

[0086] Based on the modulus of the three-phase current fault components and the modulus of the three-phase voltage of each switch, the cosine similarity coefficient of each switch is obtained.

[0087] Based on the cosine similarity coefficients of each switch, the product of the cosine similarity coefficients of the first switch and each of the second switches is obtained, and then the sum of the cosine similarity coefficient products is obtained.

[0088] The sum of the cosine similarity coefficients is compared with the protection setting value. When the sum of the cosine similarity coefficients is less than or equal to the protection setting value, it is determined that a fault has occurred in the protection area of ​​the T-connected multi-segment line of the medium-voltage distribution network / medium-voltage microgrid. The cascade protection is activated, and the switch in the area is tripped.

[0089] The present invention will be further described in detail below with reference to specific embodiments. A multi-terminal longitudinal protection method for medium-voltage distribution networks / medium-voltage microgrids, the specific implementation steps of which are as follows:

[0090] Step S1: Number the switches of each line in the T-connected multi-terminal line protection area of ​​the medium-voltage distribution network / medium-voltage microgrid sequentially as #1, #2, #3, ..., #n. Obtain the three-phase current collected by the protection terminals of switches #1, #2, #3, ..., #n, and record them as i. A1 i B1 i C1 i A2 i B2 i C2 , ..., i An i Bn i Cn Each protection terminal calculates the time window i within s milliseconds after the fault starts. A1 i B1 i C1 i A2 i B2 i C2 , ..., i An i Bn i Cn Fault component of current Δi A1 , Δi B1 , Δi C1 ,Δi A2 , Δi B2 , ΔiC2 , …, Δi An , Δi Bn , Δi Cn ; wherein the judgment principle of the fault start is: if the three-phase current collected by any protection terminal is greater than the overcurrent element judgment constant I set , then it is judged that the fault may occur at this time, and the fault start is triggered, the protection terminal of the protection terminal sends a fault start command to the protection terminal of the other switch in the protection area, and the fault start of all switch protection terminals in the area is triggered to 1; the three-phase voltage of the #1, #2, #3, …, #n switch protection terminal fault start time point 5 cycles before the time point after s milliseconds is obtained, and is recorded as u A1 , u B1 , u C1 , u A2 , u B2 , u C2 , …, u An , u Bn , u Cn ;

[0091] The above #1 switch selection principle is: based on the design drawing of the medium voltage distribution network or the medium voltage micro-grid line topology, the voltage and current connection of each switch in the direction of the medium voltage distribution network / medium voltage micro-grid from one transformer substation is connected by default, and the power flow is out of this transformer substation; wherein the #1 switch is the switch closest to the transformer substation on the design drawing;

[0092] Step S2: Clark phase module transformation is performed on Δi A1 , Δi B1 , Δi C1 , Δi A2 , Δi B2 , Δi C2 , …, Δi An , Δi Bn , Δi Cn , respectively, to obtain the modulus of the current fault component at #1, #2, #3, …, #n switches: Clark phase module transformation is performed on u A1 , u B1 , u C1 , u A2 , u B2 , u C2 , …, u An , u Bn , u Cn , respectively, to obtain the modulus of the voltage at #1, #2, #3, …, #n switches after the fault start time point 5 cycles:

[0093] Step S3: respectively calculate the fault component modulus of current at #1, #2, #3, …, #n switches and the modulus of voltage after 5 cycles before the fault starting time t0 as Δil and ul, Δi2 and u2, …, Δin and un. n And ul n The cosine similarity coefficient cosθ k , where k represents the switch number of each connected switch in the area, k = 1, 2, 3, …, n.

[0094] S4: Calculate the cosine similarity coefficient product sum σ between #1 switch and any of #2, #3, …, #n switches, and compare it with the protection setting value σ set Compare and determine the fault location. When the cosine similarity coefficient product sum σ is less than or equal to the protection setting value σ set , it is determined as an intra-zone fault, and the protection device cuts off the fault; when the cosine similarity coefficient product sum σ is greater than the protection setting value σ set , it is determined as an extra-zone fault.

[0095] The time window s in step S1 is selected according to the sampling frequency of the protection terminal, and it is required to ensure that there are not less than 10 sampling points in the data window.

[0096] The overcurrent element judgment value I set in step S1 of the power distribution terminal can be set, and it is recommended to be set greater than the maximum load current of the medium-voltage distribution network / medium-voltage micro-grid line in the application of the protection method of the application.

[0097] The calculation formula of cosθ k in step S3 is: Wherein: k represents the switch number of each connected switch in the area, k = 1, 2, 3, …, n, and j = 1, 2, …, N, N represents the total number of sampling points in the s millisecond time window.

[0098] The calculation formula of the cosine similarity coefficient product sum σ in step S4 is: Wherein: cosθ1 is the cosine similarity coefficient at #1 switch, and cosθ m is the cosine similarity coefficient at any of #2, #3, …, #n switches.

[0099] The protection setting value σ set in step S4 is recommended to be in the range of -1 ≤ σ set < 0.

[0100] Simulation experiment

[0101] In order to verify the protection method of the application, a simulation platform based on PSCAD / EMTDC is built as shown in Figure 3The simulation model shown is for a medium-voltage distribution network / medium-voltage microgrid system containing the T-connected lines of switches #1, #2, and #3. The distribution transformers use a YnD connection, and the system is powered by 35kV / 10kV distribution transformers. The lengths of lines L1, L2, L3, L4, and L5 are 11km, 7km, 2km, 7km, and 4km respectively. L2 and L3 are pure cable lines, while the remaining AC transmission lines use the 3L1 type tower structure. The loads Load1-Load4 all have the same capacity. Fault settings: The fault starts at 0.6s and lasts for 0.1s, respectively. Figure 3 The simulation of a two-phase ground fault (BC) is performed on the fault points inside and outside the zones f1-f5 shown. f1, f4, and f5 are fault points outside the zones, while f2 and f3 are fault points inside the zones. The sampling frequency is set to 1.2kHz, the data window length is 10ms, and the number of sampling points N is 12. The σ in this simulation embodiment... set It is set to -0.9.

[0102] When a fault occurs inside or outside the zone in a T-connected line, the polarities of the fault currents of each switch are as follows: Figure 4 and Figure 5 As shown, the i1, i2, i3...i flows through the measuring points i1, i2, i3...i of switches #1, #2, #3...#n. n The polarity of the fault current and the pre-fault voltage u at switch #1 is shown in Table 1.

[0103] Table 1 Current and voltage polarity during faults inside and outside the zone.

[0104]

[0105] 1) A two-phase ground fault (BC) occurs within the area, verifying the accuracy of the proposed protection method.

[0106] Taking a two-phase ground fault (BC) at fault point f2 within the zone, with a transition resistance of 0Ω as an example, the reliability of the proposed protection method is verified through simulation. The simulation results of the line-mode components of the fault currents i1, i2, and i3 and the pre-fault voltage u are as follows: Figure 6 As shown, the cosine similarity coefficients between the fault current components and the pre-fault voltages at switches #1, #2, and #3 are as follows: Figure 7 As shown.

[0107] from Figure 6 Simulation data shows that after the fault starts, Δi1 and Δu have the same polarity, while Δi2, Δi3 and Δu have opposite polarities. Figure 7 The data shows that the cosine similarity coefficient at switch #1 tends to 1, while the cosine similarity coefficients at switches #2 and #3 tend to -1.

[0108] 2) A two-phase ground fault (BC) occurs outside the protection zone to verify the accuracy of the proposed protection method.

[0109] Taking a two-phase ground fault (BC) at fault point f1 outside the fault zone, with a transition resistance of 0Ω as an example, the reliability of the proposed protection method is verified through simulation. The simulation results of the line-mode components of the fault currents i1, i2, and i3 and the pre-fault voltage u are as follows: Figure 8 As shown, the cosine similarity coefficients between the fault current components and the pre-fault voltages at switches #1, #2, and #3 are as follows: Figure 9 As shown.

[0110] from Figure 8 Simulation data shows that after the fault starts, the polarities of Δi1, Δi2, Δi3 and Δu are all opposite. Figure 9 The data shows that the cosine similarity coefficients at switches #1, #2, and #3 all tend to be -1.

[0111] 3) Adaptability analysis of the proposed protection method under different fault locations

[0112] Taking two-phase ground faults (BCG) occurring at different fault locations f1, f2, f3, f4, and f5 inside and outside the T-connection line area, with a transition resistance of 0Ω as an example, simulations are used to verify the adaptability of the proposed protection method under different fault locations. The simulation results of the cosine similarity coefficients of Δi1, Δi2, Δi3 and Δu at switches #1, #2, and #3, as well as the product of the cosine similarity coefficients and σ, are shown in Table 2.

[0113] Table 2. Cosine similarity coefficients for different fault types and locations.

[0114]

[0115] According to the simulation data in Table 2, when faults f2 and f3 occur within the T-connected line area, the cosine similarity coefficient at switch #1 is positive, while the cosine similarity coefficients at switches #2 and #3 are negative. The sum of the cosine similarity coefficients σ is -1.6056, which is less than the protection setting value of -0.9, thus satisfying the protection criterion. Therefore, the protection device should immediately clear the fault. When faults f1, f4, and f5 occur outside the T-connected line area, the sum of the cosine similarity coefficients σ is greater than the protection setting value of -0.9, thus not satisfying the protection criterion, and the protection should reset.

[0116] 4) Protection adaptability analysis under different transition resistances

[0117] Taking a two-phase ground fault (BC) at point f2 in the zone as an example, with transition resistances of 0Ω, 50Ω, 100Ω, 150Ω, and 200Ω respectively, the adaptability of the proposed protection method under different transition resistances is verified by simulation, as shown in Table 3.

[0118] Table 3 Cosine similarity coefficients under different transition resistances

[0119]

[0120] According to the simulation data in Table 3, when the transition resistance increases from 0 to 200Ω, the cosine similarity coefficient product and σ first decreases and then increases, and when the transition resistance is 200Ω, the cosine similarity coefficient product and σ is still far less than the protection setting value-0.9, so the protection method has strong transition resistance resistance.

[0121] The embodiment of the application also provides a medium-voltage distribution network / medium-voltage micro-grid multi-terminal longitudinal protection system, comprising,

[0122] The three-phase current fault component and three-phase voltage acquisition module is configured to acquire three-phase current fault components and three-phase voltages at each switch in a medium-voltage distribution network / medium-voltage micro-grid T-connected multi-terminal line protection area within a time window; wherein the switch includes a first switch at a transformer substation and a second switch connected to each load respectively;

[0123] The modulus acquisition module is configured to obtain the modulus of the three-phase current fault component and the modulus of the three-phase voltage of each switch according to the three-phase current fault component and the three-phase voltage;

[0124] The cosine similarity coefficient acquisition module is configured to obtain the cosine similarity coefficient of each switch according to the modulus of the three-phase current fault component and the modulus of the three-phase voltage of each switch;

[0125] The cosine similarity coefficient product and acquisition module is configured to obtain the cosine similarity coefficient product of the first switch and each second switch according to the cosine similarity coefficient of each switch, and further obtain the cosine similarity coefficient product and; and,

[0126] The fault judgment and processing module is configured to compare the cosine similarity coefficient product and with a protection setting value, when the cosine similarity coefficient product and is less than or equal to the protection setting value, it is judged that a fault occurs in the medium-voltage distribution network / medium-voltage micro-grid T-connected multi-terminal line protection area, and the longitudinal protection acts to trip the switch in the area; when the cosine similarity coefficient product and is greater than the protection setting value, it is judged as an external fault, and the corresponding area will be handled automatically.

[0127] The three-phase current fault component and three-phase voltage acquisition module acquires three-phase current fault components at each switch in a medium-voltage distribution network / medium-voltage micro-grid T-connected multi-terminal line protection area within a time window, comprising,

[0128] Acquiring a fault starting time;

[0129] Acquiring three-phase currents at each switch in a medium-voltage distribution network / medium-voltage micro-grid T-connected multi-terminal line protection area within a time window starting from the fault starting time;

[0130] According to the three-phase current, the three-phase current fault component at each switch is obtained.

[0131] wherein, the three-phase current fault component and three-phase voltage obtaining module obtains three-phase voltage at each switch in the T-connected multi-terminal line protection area of the medium voltage distribution network / medium voltage micro-grid in a time window, including,

[0132] obtaining a fault starting time;

[0133] obtaining three-phase voltage at each switch in the T-connected multi-terminal line protection area of the medium voltage distribution network / medium voltage micro-grid in a time window starting from a set time period before the fault starting time.

[0134] wherein, the fault starting time is obtained, including,

[0135] obtaining three-phase current at each switch;

[0136] comparing the three-phase current at each switch with an overcurrent element judgment constant value, if the three-phase current at at least one switch is greater than the overcurrent element judgment constant value, the current time is the fault starting time.

[0137] wherein, the overcurrent element judgment constant value is set as the maximum load current of the medium voltage distribution network / medium voltage micro-grid line.

[0138] wherein, the module obtaining module obtains the modulus of three-phase current fault component at each switch according to the three-phase current fault component and three-phase voltage, including,

[0139] according to three-phase current fault component Δi Ak , Δi Bk , Δi Ck of a certain switch k, performing Clark phase module transformation,

[0140]

[0141] obtaining the modulus of three-phase current fault component Δi k at the switch k.

[0142] the module obtaining module obtains the modulus of three-phase voltage at each switch according to the three-phase current fault component and three-phase voltage, including,

[0143] according to three-phase voltage u Ak , u Bk , u Ck of a certain switch k, performing Clark phase module transformation,

[0144]

[0145] obtaining the modulus of three-phase voltage u k at the switch k.

[0146] The cosine similarity coefficient obtaining module obtains the cosine similarity coefficient of each switch according to the modulus of the three-phase current fault component and the modulus of the three-phase voltage of each switch, including,

[0147] According to the modulus of the three-phase current fault component of a certain switch k i and the modulus of the three-phase voltage u i , the following operation is performed,

[0148]

[0149] The cosine similarity coefficient cosθ of the switch k is obtained k ; wherein j = 1, 2…N, and N represents the total number of sampling points in the time window.

[0150] The embodiment of the present application also provides another computer device, including a processor and a memory configured to store a computer program capable of running on the processor; wherein the processor is configured to run the computer program, and execute the method steps in the foregoing embodiments.

[0151] In actual application, the processor includes a field programmable gate array (FPGA), and the processor can be a central processing unit (CPU) or a digital signal processor (DSP). It can be understood that for different devices, the electronic device for realizing the function of the processor can also be other devices, and the embodiment of the present application is not limited specifically.

[0152] The memory can be a volatile memory (volatile memory), such as a random access memory (RAM), or a non-volatile memory (non-volatile memory), such as a read-only memory (ROM), a flash memory, a hard disk (HDD) or a solid state disk (SSD), or a combination of the above types of memories, and provides instructions and data to the processor.

[0153] In an exemplary embodiment, the embodiment of the present application also provides a computer readable storage medium for storing a computer program.

[0154] Optionally, the computer readable storage medium can be applied to any one of the methods in the embodiments of the present application, and the computer program makes the computer execute the corresponding processes realized by the processor in each method of the embodiments of the present application. For the sake of brevity, it will not be repeated here.

[0155] In several embodiments provided by the present application, it should be understood that the disclosed devices and methods can be implemented in other manners. The embodiments described above are merely exemplary, for example, the division of the units is only a logical function division, and there can be another division manner in actual implementation, for example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed coupling, direct coupling or communication connection between the components can be indirect coupling or communication connection through some interfaces, devices or units, and can be electrical, mechanical or in other forms.

[0156] Those skilled in the art understand that the embodiments of the present application can be provided as a method, a system or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer usable program code. The solutions in the embodiments of the present application can be implemented in various computer languages, such as object-oriented programming language Java and interpreted scripting language JavaScript.

[0157] The present application is described with reference to flowcharts and / or block diagrams of methods, devices (systems) and computer program products according to embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams can be realized by computer program instructions. These computer program instructions can be provided to a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to produce a machine, so that the instructions executed by the computer or other programmable data processing device produce a device implemented in the flowcharts and / or block diagrams. Figure 1 The device for implementing the functions specified in one flow or multiple flows and / or blocks Figure 1 The device for implementing the functions specified in one flow or multiple flows and / or blocks

[0158] These computer program instructions can also be stored in a computer readable storage medium capable of guiding the computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable storage medium produce a product including instruction devices, which implement the functions specified in the flowcharts and / or block diagrams. Figure 1one or more processes and / or blocks Figure 1 the function specified in the one or more blocks or blocks.

[0159] These computer program instructions can also be loaded into computer or other programmable data processing devices to cause a series of operational steps to be performed on the computer or other programmable devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable devices provide steps for implementing the process Figure 1 one or more processes and / or blocks Figure 1 the function specified in the one or more blocks or blocks.

[0160] While the preferred embodiments of the application have been described, additional variations and modifications can be made to the preferred embodiments by those skilled in the art once they learn of the basic inventive concepts. Therefore, the appended claims are intended to cover all such additional variations and modifications as fall within the scope of the application. What is claimed is:

[0161] Obviously, numerous modifications and variations of the present application are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims and their equivalents, the application can be practiced otherwise than as specifically described.

Claims

1. A multi-terminal longitudinal protection method for medium-voltage distribution networks / medium-voltage microgrids, characterized in that: include, The three-phase current fault components and three-phase voltages at each switch in the T-connected multi-terminal line protection area of ​​the medium-voltage distribution network / medium-voltage microgrid within a certain time window are obtained; wherein, the switch includes a first switch on the substation side and a second switch connected to each load respectively; Based on the three-phase current fault components and three-phase voltages, the modulus of the three-phase current fault components and the modulus of the three-phase voltages of each switch are obtained. Based on the modulus of the three-phase current fault components and the modulus of the three-phase voltage of each switch, the cosine similarity coefficient of each switch is obtained. Based on the cosine similarity coefficients of each switch, the product of the cosine similarity coefficients of the first switch and each of the second switches is obtained, and then the sum of the cosine similarity coefficient products is obtained. The sum of the cosine similarity coefficients is compared with the protection setting value. When the sum of the cosine similarity coefficients is less than or equal to the protection setting value, it is determined that a fault has occurred in the protection area of ​​the T-connected multi-terminal line of the medium-voltage distribution network / medium-voltage microgrid. The longitudinal protection is activated, and the switch in the area is tripped.

2. The method as described in claim 1, characterized in that: Acquire the three-phase current fault components at each switch in the protection zone of the T-connected multi-terminal line of the medium-voltage distribution network / medium-voltage microgrid within a certain time window, including: Obtain the fault start time; Obtain the three-phase current at each switch in the T-connected multi-terminal line protection area of ​​the medium-voltage distribution network / medium-voltage microgrid within a time window starting from the fault initiation time; Based on the three-phase current, the fault components of the three-phase current at each switch are obtained.

3. The method as described in claim 1, characterized in that: Acquire the three-phase voltage at each switch in the T-connected multi-terminal line protection area of ​​the medium-voltage distribution network / medium-voltage microgrid within a certain time window, including: Obtain the fault start time; The three-phase voltage at each switch in the T-connected multi-terminal line protection area of ​​the medium-voltage distribution network / medium-voltage microgrid is obtained within a time window starting from a set time period before the fault initiation time.

4. The method as described in claim 2 or 3, characterized in that: Obtain the fault start time, including, Obtain the three-phase current at each switch; The three-phase current at each switch is compared with the overcurrent element judgment set value. If the three-phase current at at least one switch is greater than the overcurrent element judgment set value, the current moment is the fault start moment.

5. The method as described in claim 4, characterized in that: The overcurrent element judgment setting is set to the maximum load current of the medium-voltage distribution network / medium-voltage microgrid line.

6. The method as described in claim 1, characterized in that: Based on the three-phase current fault components and the three-phase voltage, the modulus of the three-phase current fault components of each switch is obtained, including: Based on the three-phase current fault component Δi of a certain switch k Ak , Δi Bk , Δi Ck Perform Clark phase mode transformation. The modulus Δi of the three-phase current fault component at switch k is obtained. k ; Based on the three-phase current fault components and three-phase voltages, the modulus of the three-phase voltages of each switch is obtained, including: Based on the three-phase voltage u of a certain switch k Ak u Bk u Ck Perform Clark phase mode transformation. Obtain the modulus u of the three-phase voltage at switch k. k .

7. The method as described in claim 1, characterized in that: Based on the modulus of the three-phase current fault components and the modulus of the three-phase voltages of each switch, the cosine similarity coefficient of each switch is obtained, including: Based on the modulus Δi of the three-phase current fault component of a certain switch k i And the modulus u of three-phase voltage i Perform the following calculations. Obtain the cosine similarity coefficient cosθ of switch k k Where j = 1, 2...N, and N represents the total number of sampling points within the time window.

8. A multi-terminal longitudinal protection system for medium-voltage distribution networks / medium-voltage microgrids, characterized in that: include, The three-phase current fault component and three-phase voltage acquisition module is configured to acquire the three-phase current fault component and three-phase voltage at each switch in the T-connected multi-terminal line protection area of ​​the medium-voltage distribution network / medium-voltage microgrid within a certain time window; wherein, the switch includes a first switch on the substation side and a second switch connected to each load respectively. The modulus acquisition module is configured to obtain the modulus of the three-phase current fault component and the modulus of the three-phase voltage of each switch based on the three-phase current fault component and the three-phase voltage. The cosine similarity coefficient acquisition module is configured to obtain the cosine similarity coefficient of each switch based on the modulus of the three-phase current fault component and the modulus of the three-phase voltage of each switch. The cosine similarity coefficient product sum acquisition module is configured to obtain the product of the cosine similarity coefficients of the first switch and each of the second switches based on the cosine similarity coefficients of each switch, and then obtain the sum of the cosine similarity coefficient products; and, The fault judgment and processing module is configured to compare the sum of the cosine similarity coefficients with the protection setting value. When the sum of the cosine similarity coefficients is less than or equal to the protection setting value, it is determined that a fault has occurred in the protection area of ​​the T-connected multi-terminal line of the medium-voltage distribution network / medium-voltage microgrid, and the longitudinal protection is activated to trip the switch in the area.

9. The system as described in claim 8, characterized in that: The three-phase current fault component and three-phase voltage acquisition module acquires the three-phase current fault components at each switch in the T-connected multi-terminal line protection area of ​​the medium-voltage distribution network / medium-voltage microgrid within a certain time window, including: Obtain the fault start time; Obtain the three-phase current at each switch in the T-connected multi-terminal line protection area of ​​the medium-voltage distribution network / medium-voltage microgrid within a time window starting from the fault initiation time; Based on the three-phase current, the fault components of the three-phase current at each switch are obtained.

10. The system as described in claim 8, characterized in that: The three-phase current fault component and three-phase voltage acquisition module acquires the three-phase voltage at each switch in the T-connected multi-terminal line protection area of ​​the medium-voltage distribution network / medium-voltage microgrid within a certain time window, including... Obtain the fault start time; The three-phase voltage at each switch in the T-connected multi-terminal line protection area of ​​the medium-voltage distribution network / medium-voltage microgrid is obtained within a time window starting from a set time period before the fault initiation time.

11. The system as described in claim 9 or 10, characterized in that: Obtain the fault start time, including, Obtain the three-phase current at each switch; The three-phase current at each switch is compared with the overcurrent element judgment set value. If the three-phase current at at least one switch is greater than the overcurrent element judgment set value, the current moment is the fault start moment.

12. The system as described in claim 11, characterized in that: The overcurrent element judgment setting is set to the maximum load current of the medium-voltage distribution network / medium-voltage microgrid line.

13. The system as described in claim 8, characterized in that: The modulus acquisition module obtains the modulus of each switch's three-phase current fault component based on the three-phase current fault components and the three-phase voltage, including: Based on the three-phase current fault component Δi of a certain switch k Ak , Δi Bk , Δi Ck Perform Clark phase mode transformation. The modulus Δi of the three-phase current fault component at switch k is obtained. k ; The modulus acquisition module obtains the modulus of the three-phase voltage of each switch based on the three-phase current fault components and the three-phase voltage, including: Based on the three-phase voltage u of a certain switch k Ak u Bk u Ck Perform Clark phase mode transformation. Obtain the modulus u of the three-phase voltage at switch k. k .

14. The system as described in claim 8, characterized in that: The cosine similarity coefficient acquisition module obtains the cosine similarity coefficient of each switch based on the modulus of the three-phase current fault component and the modulus of the three-phase voltage, including: Based on the modulus Δi of the three-phase current fault component of a certain switch k i And the modulus u of three-phase voltage i Perform the following calculations. Obtain the cosine similarity coefficient cosθ of switch k k Where j = 1, 2...N, and N represents the total number of sampling points within the time window.

15. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor; characterized in that: When the processor executes the computer program, it implements the steps of the multi-terminal longitudinal protection method for medium-voltage distribution networks / medium-voltage microgrids as described in any one of claims 1 to 7.

16. A computer-readable storage medium storing a computer program; characterized in that: When the computer program is executed by the processor, it implements the steps of the multi-terminal longitudinal protection method for medium-voltage distribution networks / medium-voltage microgrids as described in any one of claims 1 to 7.

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