A method for active power distribution network fault location and line protection independent of power supply characteristics

Abstract

The application discloses a kind of active power distribution network fault location and line protection method independent of power supply characteristics, comprising the following steps: S1, measure local protection voltage, compare the fluctuation energy of local protection voltage with preset energy threshold value, whether the fault response is started according to the comparison result, if the fault response is started, then enter step S2;S2, consider the condition of distributed energy access, calculate the zero sequence component of local protection;S3, according to the zero sequence equivalent network column write fault distance solving equation, solve the distance from local protection to fault point;S4, according to the distance from local protection to fault point solved, judge fault section, and execute corresponding protection action.The application takes zero sequence component as fault characteristic quantity, according to the zero sequence network characteristics after DG access, the method is not affected by the output characteristics of DG, the calculation process is simple, and has higher practicability.

Description

Technical Field

[0001] This invention mainly relates to the field of power grid technology, specifically to a method for fault location and line protection in active distribution networks that is independent of power supply characteristics. Background Technology

[0002] The distribution network plays a crucial role in the entire power system. With continuous social development and rising productivity, electricity consumption, as a primary energy source, is increasing daily, leading to higher demands on the reliability, security, and power quality of the distribution network. The expanding scale and increasingly complex topology of distribution networks result in a persistently high probability of faults. Therefore, it is essential to take necessary measures to locate and isolate faults and restore power to non-faulty areas. Distributed generation (DG), primarily powered by clean energy sources such as photovoltaics and wind power, is increasingly prevalent in distribution networks. DG is typically connected at the middle or end of lines, mainly near users or loads. However, as the power grid expands, DG penetration is increasing, exhibiting characteristics different from traditional distribution networks in terms of power flow distribution, fault current amplitude, direction, and distribution, thus increasing the complexity of fault detection and control.

[0003] Currently, fault location in distribution networks mainly relies on distribution automation technology. Based on different location principles, fault location methods can be categorized into matrix methods, fault analysis methods, and artificial intelligence methods. Matrix methods are simple, effective, and fast, but because their matrix elements are fault characteristic quantities, they require extremely high accuracy, resulting in poor fault tolerance and limited application scenarios. Artificial intelligence methods have better fault tolerance and can be used in complex situations with multiple concurrent faults and changing network structures, but their adaptability is poor. Fault analysis methods extract features from relevant system parameters and detected electrical quantities, such as voltage and current, and combine this with corresponding calculations to determine the location. They are theoretically sound and adaptable, but require analysis of complex distribution networks. In summary, there is an urgent need to propose a fault location and protection method that is unaffected by distributed generation (DG) and adapted to new distribution networks. Summary of the Invention

[0004] In view of the technical problems existing in the prior art, the present invention provides a simple and easy-to-operate method for active power distribution network fault location and line protection that is independent of power supply characteristics.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0006] A method for fault location and line protection in an active distribution network that is independent of power supply characteristics, comprising the following steps:

[0007] S1. Measure the voltage at the local protection point, compare the fluctuation energy of the voltage at the local protection point with the preset energy threshold value, and determine whether to start the fault response based on the comparison result. If the fault response is started, proceed to step S2.

[0008] S2. Considering the case of distributed energy access, calculate the zero-sequence component at the local protection point;

[0009] S3. Write the fault distance solution equation based on the zero-sequence equivalent network, and solve for the distance from the local protection to the fault point;

[0010] S4. Determine the faulty section based on the distance from the local protection to the fault point, and execute the corresponding protection action.

[0011] Preferably, in step S1, the specific formula for calculating the voltage fluctuation energy at the local protection point is as follows:

[0012] E V (k)=(U P (k)-U P (k-1)) 2

[0013] Among them, E V (k) represents the voltage fluctuation energy at sampling point k, U P (k) and U P (k-1) represent the voltages of adjacent points at the protection point.

[0014] Preferably, in step S1, when the comparison structures for n consecutive times all satisfy E V (k)=(U P (k)-U P (k-1)) 2 >E set If E is selected, a line fault is determined, and a fault response is initiated; where E set This is a preset energy threshold value; n takes values ​​from 3 to 8.

[0015] Preferably, in step S2, the process of calculating the zero-sequence component at the local protection point is as follows:

[0016] Assume the three-phase fault current injected into the fault point is i a ′、i b ′ and i c If ′, then the three-phase current sensed at the protection point is: I A =i a +i a ′、I B =i b +i b ′、I C =i c +i cIf ′, then the zero-sequence current at the protection point is:

[0017]

[0018] in, To protect against zero-sequence current, and These are the phasors of the three-phase currents.

[0019] Preferably, in step S2, the distributed energy source still outputs symmetrical three-phase current after the fault, specifically:

[0020]

[0021] Among them, i a i b and i c These represent the three-phase output currents; i * d and i * q These are the reference values ​​for the d-axis and q-axis, respectively; ω is the angular velocity of the power frequency quantity, and θ is the reference value for the d-axis and q-axis, respectively. PLL For synchronous angular velocity, For i * q and i * d The angle between them

[0022] Preferably, the specific process of step S3 is as follows:

[0023] During the fault transient, the following equations are written based on the zero-order network:

[0024]

[0025] in, and These represent the real parts of the zero-sequence voltage and zero-sequence current measured by the protection system, respectively. and These represent the imaginary parts of the zero-sequence voltage and zero-sequence current measured by the protection system, respectively. r1 and l1 are the unit resistance and inductance of the line, respectively. f To protect the distance from P to the fault point;

[0026] Based on data from two different sampling points, the formula is solved to obtain the distance l from the protection P to the fault point. f .

[0027] Preferably, the specific process of step S4 is as follows:

[0028] The fault section is located by solving for the distance from the protection point to the fault point. Let l be the distance from the protection point P to the fault point. f=DIS_F, design the following first action criterion:

[0029] DIS_F<Δ1

[0030] Among them, Δ1 is the action criterion for protection;

[0031] If the first action criterion is met, the local protection will trip immediately; otherwise, the second action criterion will be applied:

[0032] DIS_F<Δ2

[0033] Among them, Δ2 is the action criterion for the two-stage protection;

[0034] If the second action criterion is met, then local protection waits for a delay t. d If the circuit breaker trips, the protection will reset; otherwise, it will reset.

[0035] Preferably, in step S4, Δ1 is 0.8L. e ~0.85L e Δ2 is taken as 1.1L e ~1.2L e L e This is the total length of the line at this end.

[0036] The present invention also discloses a computer-readable storage medium having a computer program stored thereon, the computer program performing the steps of the method described above when run by a processor.

[0037] The present invention further discloses a computer device including a memory and a processor interconnected thereon, wherein the memory stores a computer program that, when run by the processor, performs the steps of the method described above.

[0038] Compared with the prior art, the advantages of the present invention are as follows:

[0039] This invention provides an active power distribution network fault location and line protection method independent of power supply characteristics. It calculates the distance from the protection installation point to the fault point under line grounding faults, thereby locating the fault section and finally isolating the fault through protection action. The method uses zero-sequence components as fault characteristic quantities. Based on the characteristics of the zero-sequence network after DG (Distributed Generation) integration, this method is unaffected by the output characteristics of the DG. The fault distance calculation equation is written based on the zero-sequence network, offering strong interpretability. Furthermore, the solution requires only two sampling points, making the calculation process simple and highly practical. Attached Figure Description

[0040] Figure 1 This is a topology diagram of the active power distribution network in this invention.

[0041] Figure 2This is a flowchart of the active power distribution network fault location and line protection method that is independent of power supply characteristics according to the present invention.

[0042] Figure 3 The following are simulation diagrams of the transient voltage and fluctuation energy of the fault phase during a fault in this invention; where (a) is the transient voltage diagram and (b) is the fluctuation energy diagram.

[0043] Figure 4 This is a simulation diagram of the zero-sequence current of the protection on both sides of the fault point in this invention during a fault.

[0044] Figure 5 This is a schematic diagram of the equivalent circuit for grounding faults according to the present invention. Detailed Implementation

[0045] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0046] like Figure 1 As shown, the active distribution network has a radial network structure with 4 nodes connected by power lines; it is connected to three different distributed energy sources (DG): wind power, photovoltaic power, and energy storage; there are 3 load branches, and all three DG sources are inverter-type power sources.

[0047] like Figure 2 As shown, the active power distribution network fault location and line protection method independent of power supply characteristics provided in this embodiment of the invention specifically includes the following steps:

[0048] S1. Measure the voltage at the local protection point, compare the fluctuation energy of the voltage at the local protection point with the preset energy threshold value, and determine whether to start the fault response based on the comparison result. If the fault response is started, proceed to step S2.

[0049] S2. Considering the case of distributed energy access, calculate the zero-sequence component at the local protection point;

[0050] S3. Write the fault distance solution equation based on the zero-sequence equivalent network, and solve for the distance from the local protection to the fault point;

[0051] S4. Determine the faulty section based on the distance from the local protection to the fault point, and execute the corresponding protection action.

[0052] Specifically, step S1 involves the following process: The distribution network has numerous feeders, forming a multi-node network. Distributed generation (DG) sources are connected to the nodes of the distribution network in a decentralized manner. Ground faults account for over 90% of the faults in the distribution network, and voltage drops are detected when a fault occurs. Although DGs actively support node voltage during faults, there is a noticeable voltage waveform during the transition from fault drop to active support.

[0053] Based on the measured voltage change, a starting criterion based on voltage fluctuation energy can be designed as follows:

[0054] E V (k)=(U P (k)-U P (k-1)) 2 >E set (1)

[0055] Among them, E V (k) represents the voltage fluctuation energy at sampling point k, U P (k) and U P (k-1) represent the voltages of adjacent points at the protection point, E set This is the threshold value for energy.

[0056] Normally, when five consecutive sampling points satisfy criterion (1), it is determined that a line fault has occurred. At the same time, the first point is recorded as the fault zero moment, and the process proceeds to step S2.

[0057] Specifically, step S2 involves the following process: First, the zero-sequence component at the local protection point is calculated, and the line fault current waveform changes after the DG is connected. DGs are mainly inverter-type power sources such as photovoltaic, direct-drive wind power, and fuel cells. The output performance of inverter-type DGs mainly depends on the inverter control response. Unlike synchronous generator power sources, DGs can still output symmetrical three-phase currents after a fault, specifically:

[0058]

[0059] Among them, i a i b and i c These represent the three-phase output currents; i * d and i * q These are the reference values ​​for the d-axis and q-axis, respectively; ω is the angular velocity of the power frequency quantity, and θ is the reference value for the d-axis and q-axis, respectively. PLL For synchronous angular velocity, for and The angle between them

[0060] Assume the three-phase fault current injected by the synchronous machine into the fault point is i. a ′、i b ′ and i c If ′, then the three-phase current sensed at the protection point is: I A =i a +i a ′、I B =i b +i b ′、I C =ic +i c If ′, then the zero-sequence current at the protection point is:

[0061]

[0062] in, Zero-sequence current at the protection point and These are the phasors of the three-phase currents.

[0063] Specifically, step S3 includes: Inverter-type DGs typically use a delta / star connection for grid connection. This method can hinder the transmission of zero-sequence current between the DG and the system, thus not affecting the zero-sequence current under grid-side faults. Selecting the zero-sequence component as a feature extraction quantity to solve for the fault distance can avoid the influence of inverter power supply characteristics.

[0064] Taking a ground fault in a certain section of the line as an example, such as Figure 5 As shown, according to Figure 5 We can obtain:

[0065]

[0066] in, To protect the voltage phasor of P, Z1 is the equivalent impedance from the protection P to the fault point. To protect the current phasor of P, R f This is the transition resistance.

[0067] Current on both sides of the circuit and Caused by the voltage at the fault location:

[0068]

[0069] As can be seen from the above equation, the currents on both sides and The phase angles δ1 and δ2 are mainly related to the zero-sequence impedances on both sides. In the system, the zero-sequence impedances on both sides can be approximately equivalent to the zero-sequence impedance angles of the transformers on both sides. Therefore, δ1≈δ2 holds true, and thus:

[0070]

[0071] Where R1 and L1 are the equivalent resistance and reactance from the protection P to the fault point, respectively, ω1 is the angular velocity of the signal, and k c is the current coefficient.

[0072] During the fault transient, the following equations can be written based on the zero-order network:

[0073]

[0074] in, and These represent the real parts of the zero-sequence voltage and zero-sequence current measured by the protection system, respectively. and These represent the imaginary parts of the zero-sequence voltage and zero-sequence current measured by the protection system, respectively. r1 and l1 are the unit resistance and inductance of the line, respectively. f To protect the distance from P to the fault point.

[0075] Equation (7) contains two equations, and both exist simultaneously. f k c and R f There are a total of 3 unknowns. During the calculation, based on data from two different sampling points, 4 equations can be obtained, which can then be used to solve for the 3 unknown parameters, and ultimately determine the distance l from the protection device P to the fault point. f .

[0076] Specifically, step S4 includes: locating the fault section based on the calculated distance from the protection installation location to the fault point, letting l f =DIS_F, design the following action criteria:

[0077] DIS_F<Δ1 (8)

[0078] Where Δ1 is the action criterion for a protection segment, assuming the total length of the line at this end is L. e Therefore, Δ1 is generally taken as 0.8L. e ~0.85L e .

[0079] If the criterion of equation (8) is met, the local protection will trip immediately; otherwise, the following judgment will be made:

[0080] DIS_F<Δ2 (9)

[0081] Among them, Δ2 is the action criterion for the two-stage protection, and Δ2 is generally taken as 1.1L. e ~1.2L e .

[0082] If the criterion of equation (9) is true, then the local protection waits for a delay t. d If the circuit breaker trips, the protection will reset; otherwise, it will reset.

[0083] This invention provides an active power distribution network fault location and line protection method independent of power supply characteristics. It calculates the distance from the protection installation point to the fault point under line grounding faults, thereby locating the fault section and finally isolating the fault through protection action. The method uses zero-sequence components as fault characteristic quantities. Based on the characteristics of the zero-sequence network after DG (Distributed Generation) integration, this method is unaffected by the output characteristics of the DG. The fault distance calculation equation is written based on the zero-sequence network, offering strong interpretability. Furthermore, the solution requires only two sampling points, making the calculation process simple and highly practical.

[0084] In practical applications, a system like PSCAD / EMTDC can be built... Figure 1 The active power distribution network model is shown. The sampling frequency of the measuring device is set to 10kHz. Let the energy storage power source, photovoltaic power source, and wind power source be DG1, DG2, and DG3, respectively. The simulation system parameters are shown in Table 1.

[0085] Table 1 Simulation System Parameters

[0086]

[0087] At a typical location at the midpoint of line L1, an A-phase metallic ground fault F is set up. The transient voltage and voltage fluctuation energy measured at protection P1-1 before and after the fault are as follows: Figure 3 As shown in (a) and (b).

[0088] It is evident that after phase A was grounded, the phase voltage rapidly dropped to a lower value, showing a significant change compared to the phase voltage before the fault. The voltage fluctuation energy exhibits a high amplitude in the initial stage of the fault, with distinct characteristics; its amplitude rapidly exceeds E... set1 The fault zero point is located at 20.1ms, which shows that the startup criterion can respond quickly to faults.

[0089] At a typical location at the midpoint of line L1, a ground fault with a 50-ohm transition resistance for phase A is set up. Calculate the zero-sequence current at protection points P1-1 and P1-2 respectively. Figure 4 As shown.

[0090] Depend on Figure 4 Although the difference in amplitude of the zero-sequence current of the protection devices on both sides of the fault point is large, the difference in phase is very small. According to... Figure 5 Given the equivalent circuit diagram of the ground fault shown, write the equation for determining the fault distance. Based on the zero-sequence voltage measured at protection point P1-1... and zero-sequence current Based on the zero point of the fault, two sets of data, k1=20, k2=40 and k′1=60, k′2=80, were used to solve for the three unknown parameters. The results are shown in Table 2.

[0091] Table 2 Results of solving unknown parameters

[0092] parameter <![CDATA[k1=20k2=40]]> <![CDATA[k′1=60k′2=80]]> DIS_F / km 5.63 5.48 <![CDATA[R f / Oh]]> 49.63 50.19 <![CDATA[k c ]]> 0.75 0.81

[0093] Based on the preceding analysis, Δ1 is taken as 0.85L in this example. e Δ2 is taken as 1.1L e Then the threshold values ​​corresponding to P1-1 are Δ1 = 9.35 and Δ2 = 12.1.

[0094] As shown in Table 2, when using differentiated data sets composed of different sampling points after a fault to solve for unknown parameters, the differentiated data sets will cause slight errors in the parameter solution results during numerical calculation. However, in the case of a fault within the line area, DIS_F > Δ1 still exists, allowing for a normal response. Reducing the protection range within one protection stage ensures selectivity, while expanding the protection range within two stages ensures coverage of faults along the entire line length.

[0095] Furthermore, since this example can directly access the transition resistor R... f The solution is obtained by performing the calculation, therefore this method is not affected by the transition resistance and can respond to high-resistance faults.

[0096] The present invention also discloses a computer-readable storage medium having a computer program stored thereon, the computer program performing the steps of the method described above when run by a processor.

[0097] The present invention further discloses a computer device including a memory and a processor interconnected thereon, wherein the memory stores a computer program that, when run by the processor, performs the steps of the method described above.

[0098] The medium and device of the present invention, corresponding to the method described above, also have the advantages described above.

[0099] The present invention can implement all or part of the processes in the methods of the above embodiments, or it can be implemented by hardware related to computer program instructions. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, it can implement the steps of the above method embodiments. The computer program includes computer program code, which can be in the form of source code, object code, executable file, or some intermediate form. The computer-readable storage medium includes: any entity or device capable of carrying computer program code, recording media, USB flash drive, portable hard drive, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. The memory is used to store computer programs and / or modules. The processor implements various functions by running or executing the computer programs and / or modules stored in the memory, and by calling data stored in the memory. The memory may include high-speed random access memory, as well as non-volatile memory, such as hard disks, RAM, plug-in hard disks, smart media cards (SMC), secure digital (SD) cards, flash cards, at least one disk storage device, flash memory device, or other volatile solid-state storage devices.

[0100] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for fault location and line protection in an active distribution network that is independent of power supply characteristics, characterized in that, Including the following steps: S1. Measure the voltage at the local protection point, compare the fluctuation energy of the voltage at the local protection point with the preset energy threshold value, and determine whether to start the fault response based on the comparison result. If the fault response is started, proceed to step S2. S2. Considering the case of distributed energy access, calculate the zero-sequence component at the local protection point; S3. Write the fault distance solution equation based on the zero-sequence equivalent network, and solve for the distance from the local protection to the fault point; S4. Determine the faulty section based on the distance from the local protection to the fault point, and execute the corresponding protection action; The specific process of step S3 is as follows: During the fault transient, the following equations are written based on the zero-order network: in, and These represent the real parts of the zero-sequence voltage and zero-sequence current measured by the protection system, respectively. and These represent the imaginary parts of the zero-sequence voltage and zero-sequence current measured by the protection system, respectively. and For the unit resistance and inductance of the circuit, To protect the distance from P to the fault point; For transition resistance; The current coefficient; The angular velocity of the signal; Based on data from two different sampling points, the formula is solved to obtain the distance from the protection P to the fault point. .

2. The active distribution network fault location and line protection method independent of power supply characteristics according to claim 1, characterized in that, In step S1, the specific formula for calculating the voltage fluctuation energy at the local protection point is as follows: in, Sampling points k Voltage fluctuation energy, and These represent the voltages at adjacent points of the protection device.

3. The active distribution network fault location and line protection method independent of power supply characteristics according to claim 2, characterized in that, In step S1, when the comparison structure satisfies n consecutive times... If a line fault is detected, a fault response is initiated; whereby... This is a preset energy threshold value; n takes values ​​from 3 to 8.

4. The active distribution network fault location and line protection method independent of power supply characteristics according to claim 1, 2, or 3, characterized in that, In step S2, the process of calculating the zero-sequence component at the local protection point is as follows: Assume the three-phase fault current injected into the fault point is , and The three-phase current sensed at the protection point is: , , The zero-sequence current at the protection point is: in, To protect against zero-sequence current, , and These are the phasors of the three-phase currents; , and These represent the three-phase output currents.

5. The active distribution network fault location and line protection method independent of power supply characteristics according to claim 4, characterized in that, In step S2, the distributed energy source still outputs symmetrical three-phase current after the fault, specifically: in, and These are the reference values ​​for the d-axis and q-axis, respectively. Angular velocity, which is a power frequency quantity. For synchronous angular velocity, for and The angle between them .

6. The active distribution network fault location and line protection method independent of power supply characteristics according to claim 1, 2, or 3, characterized in that, The specific process of step S4 is as follows: The fault section is located by solving for the distance from the protection point to the fault point. Let the distance from the protection point P to the fault point be... The first action criterion is designed as follows: in, A criterion for determining a protective action; If the first action criterion is met, the local protection will trip immediately; otherwise, the second action criterion will be applied: in, This serves as the action criterion for two-stage protection; If the second action criterion is met, local protection will wait for a certain period of time. If the circuit breaker trips, the protection will reset; otherwise, it will reset.

7. The active distribution network fault location and line protection method independent of power supply characteristics according to claim 6, characterized in that, In step S4, Take 0.8 ~0.85 ; Take 1.1 ~1.2 ; This is the total length of the line at this end.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, The computer program, when run by a processor, performs the steps of the method as described in any one of claims 1-7.

9. A computer device comprising a memory and a processor interconnected thereon, the memory storing a computer program, characterized in that, The computer program, when run by a processor, performs the steps of the method as described in any one of claims 1-7.

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