An adaptive distance protection method for phase-to-phase short circuit of distribution network with distributed power supply

Abstract

The application discloses a kind of adaptive distance protection methods of phase-to-phase short circuit of distribution network containing distributed power supply.The bus voltage and feeder outlet current of distribution network are collected, whether phase-to-phase voltage or phase voltage fault component satisfies starting criterion is judged;Whether short-circuit current negative sequence component and zero sequence component satisfy phase-to-phase short circuit fault criterion is judged;If the above criterion is satisfied, the fault phase is selected using phase current difference abrupt variable, and the upstream fault location k1 and downstream fault location k2 are calculated according to the bus negative sequence voltage of non-fault phase and the positive sequence current of non-fault phase feeder;If either upstream fault location k1 and downstream fault location k2 is less than distance protection setting value k set , it is determined that phase-to-phase short circuit fault occurs in the protection range.The application is not affected by short-circuit transient resistance, grid-connected distributed power supply capacity, system operation mode and other factors, and has the advantages of fast speed, good reliability and strong adaptability.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection, specifically to an adaptive distance protection method for phase-to-phase short circuits in distribution networks containing distributed generation sources. Background Technology

[0002] As traditional power generation methods increasingly consume and pollute environmental resources, new energy power generation, as a less polluting and highly renewable method, is gaining increasing attention. Distributed generation, in particular, is widely integrated into distribution networks due to its simple structure and convenient installation. However, due to the influence of inverter control strategies, distributed generation often exhibits characteristics such as weak feedback and controlled current phase, leading to the risk of failure in relay protection systems in the distribution network, such as adaptive current protection and differential current protection.

[0003] Currently, researchers are studying relay protection for distribution networks containing distributed generation (DG) sources, primarily including adaptive current protection based on DG equivalent models and iterative algorithms, and differential current protection for distribution networks based on multiple criteria. However, these protection methods suffer from drawbacks such as high protection delay and reliance on device communication. Compared to existing protection methods, distance protection calculates and measures impedance and compares it with protection settings to achieve fault location and protection output, offering advantages such as fast response speed and independence from system operating conditions. However, distance protection for distribution networks with DG integration suffers from poor resistance to transition resistance and branch coefficient failure. To address these issues, some scholars have improved the calculation formula for distance protection branch coefficients based on composite sequence networks. While this method enhances the reliability of distance protection, it requires acquiring the fault current output by the DG, resulting in high costs and limited practicality. Other scholars have proposed a distance protection fault location method based on the sine theorem, which can accurately calculate the fault location on the line, but it is not applicable to distribution networks with multiple DG sources, lacking practical engineering applicability.

[0004] In summary, due to the weak feed and phase-controlled characteristics of distributed generation (DG), existing distribution network protection systems are prone to failure, including malfunctions or failures to operate. Current DG-based distribution network protection systems suffer from high costs, overly idealized application scenarios, and limited applicability; therefore, there is currently no effective protection method for DG-based distribution networks. Consequently, developing a highly sensitive and reliable protection method for DG-based distribution networks has become a pressing issue for those skilled in the art. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention provides an adaptive distance protection method for phase-to-phase short circuits in distribution networks containing distributed power sources. This method solves the technical problem that there is currently no effective method for protecting phase-to-phase short circuit faults in distribution networks containing distributed power sources. It can accurately protect phase-to-phase short circuit faults under different distributed power source capacities, system operating modes, and fault locations, and is not affected by the transition resistance at the short circuit point. It has high reliability and practicality.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution, including the following steps:

[0007] S101: Collects the voltage of the distribution network bus and the current output of each feeder;

[0008] S102: Calculate the phase-to-phase voltage and the phase voltage fault component. If the phase-to-phase voltage and the phase voltage fault component meet the protection start-up criterion, execute step S103; otherwise, determine that no fault has occurred in the distribution network and execute step S101.

[0009] S103: Use the negative sequence component and zero sequence component in the short-circuit current to determine whether the line fault is a phase-to-phase short-circuit fault. If it is determined that a phase-to-phase short circuit has occurred in the distribution network, execute step S104; otherwise, execute step S101.

[0010] S104: Use the sudden change in the three-phase current difference during a fault to determine the faulty phase;

[0011] S105: Calculate the upstream fault location k1 using the negative sequence voltage of the non-faulty phase of the busbar and the positive sequence current of the non-faulty phase at the feeder outlet;

[0012] S106: Calculate the downstream fault location k2 using the non-faulty phase negative sequence voltage of the busbar and the non-faulty phase positive sequence current at the feeder outlet;

[0013] S107: Compare the upstream fault location k1 with the distance protection setting value k set If k1≤k set If yes, then execute S109; otherwise, execute S108.

[0014] S108: Compare the downstream fault location k2 with the distance protection setting value k set If k2≤k set If the fault is found to be outside the protected area, then S109 is executed; otherwise, if the fault is determined to be outside the protected area, return to S101.

[0015] S109: It is determined that a phase-to-phase short circuit fault has occurred within the protected area.

[0016] In the adaptive distance protection method for phase-to-phase short circuits in a distribution network containing distributed generation, this invention collects the distribution network bus voltage and feeder output current to determine whether the phase-to-phase voltage or phase voltage fault component meets the start-up criteria; it also determines whether the negative-sequence component and zero-sequence component of the short-circuit current meet the phase-to-phase short-circuit fault criteria; if the above criteria are met, the faulty phase is selected using the phase current difference abrupt change, and the upstream fault location k1 and downstream fault location k2 are calculated based on the negative-sequence voltage of the non-faulty phase bus and the positive-sequence current of the non-faulty phase feeder; if either the upstream fault location k1 or the downstream fault location k2 is less than the distance protection setting value k... set If the fault occurs, it is determined that a phase-to-phase short circuit fault has occurred within the protection range.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. Existing technologies use the bus voltage and feeder outlet current of the faulty phase to calculate the measurement impedance and directly use the measured impedance to determine the fault location. This is only applicable to traditional distribution networks and cannot guarantee accuracy and sensitivity in power grids containing distributed generation. This invention provides a fault location calculation method based on the negative sequence voltage of the non-faulty phase bus and the positive sequence current of the non-faulty phase feeder. This method can realize the location and protection of phase-to-phase short-circuit faults in active distribution networks under different penetration rates of distributed generation.

[0019] 2. The protection criteria of the existing technology are constructed based on the condition of a single distributed power source connection, which lacks adaptability and reliability for multiple distributed power source connections to the feeder; the present invention is applicable to the situation where there are multiple distributed power source connections to the feeder, and phase-to-phase short circuit faults occur upstream, in the middle, and downstream of the grid connection point, and has good applicability.

[0020] 3. The sensitivity of existing technologies is easily affected by fault transition resistance, and there are problems with insufficient accuracy and sensitivity under high resistance fault conditions. This invention takes into account the influence of distributed power supply capacity, fault transition resistance and system operation mode, and uses the negative sequence voltage and positive sequence current of non-faulty phases as characteristic quantities, which can accurately calculate the location of phase-to-phase short circuit faults on the feeder and has strong resistance to transition resistance.

[0021] 4. Existing technologies mostly use communication methods to collect multi-point fault information to achieve fault protection in distribution networks with distributed power sources, which limits the application scenarios; this invention only uses power frequency voltage and current to achieve fault protection, which is simple in principle, easy to implement, and highly practical. Attached Figure Description

[0022] To make the objectives, technical solutions, and advantages of the invention clearer, the invention will now be described in further detail with reference to the accompanying drawings, wherein:

[0023] Figure 1A flowchart illustrating the adaptive distance protection method for phase-to-phase short circuits in distribution networks containing distributed generation sources;

[0024] Figure 2 This is a schematic diagram of a distribution network containing distributed generation sources;

[0025] Figure 3 This is a schematic diagram of the upstream fault location parameter k1 of a phase-to-phase short circuit in a distribution network containing distributed generation sources on different feeders.

[0026] Figure 4 This is a schematic diagram of the downstream fault location parameter k2 of a phase-to-phase short circuit in a distribution network containing distributed generation sources on different feeders.

[0027] Figure 5 A schematic diagram of the upstream fault location parameter k1 for phase-to-phase short circuits in a distribution network with distributed generation sources, under different transient resistance capabilities.

[0028] Figure 6 This is a schematic diagram of the downstream fault location parameter k2 for phase-to-phase short circuits in a distribution network containing distributed generation sources, with different transient resistance capabilities. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This specific implementation method, such as Figure 1 As shown, the adaptive distance protection method for phase-to-phase short circuits in a distribution network containing distributed generation includes the following steps:

[0031] S101: Collects the voltage of the distribution network bus and the current output of each feeder;

[0032] S102: Calculate the phase-to-phase voltage and the phase voltage fault component. If the phase-to-phase voltage and the phase voltage fault component meet the protection start-up criterion, execute step S103; otherwise, determine that no fault has occurred in the distribution network and execute step S101.

[0033] S103: Use the negative sequence component and zero sequence component in the short-circuit current to determine whether the line fault is a phase-to-phase short-circuit fault. If it is determined that a phase-to-phase short circuit has occurred in the distribution network, execute step S104; otherwise, execute step S101.

[0034] S104: Use the sudden change in the three-phase current difference during a fault to determine the faulty phase;

[0035] S105: Calculate the upstream fault location k1 using the negative sequence voltage of the non-faulty phase of the busbar and the positive sequence current of the non-faulty phase at the feeder outlet;

[0036] S106: Calculate the downstream fault location k2 using the non-faulty phase negative sequence voltage of the busbar and the non-faulty phase positive sequence current at the feeder outlet;

[0037] S107: Compare the upstream fault location k1 with the distance protection setting value k set If k1≤k set If yes, then execute S109; otherwise, execute S108.

[0038] S108: Compare the downstream fault location k2 with the distance protection setting value k set If k2≤k set If the fault is found to be outside the protected area, then S109 is executed; otherwise, if the fault is determined to be outside the protected area, return to S101.

[0039] S109: It is determined that a phase-to-phase short circuit fault has occurred within the protected area.

[0040] In this embodiment of the invention, based on a distribution network containing distributed power sources, it is necessary to collect the bus voltage and the current at each feeder outlet according to a certain sampling period. Since the specific sampling method and the corresponding sampling limitations are conventional capabilities possessed by those skilled in the art, this invention does not impose specific limitations on them.

[0041] In this embodiment of the invention, in S102, the protection activation criterion includes determining whether the line voltage fault component is greater than the line voltage threshold value or determining whether the phase voltage fault component is greater than the phase voltage threshold value. For details, please refer to the following:

[0042] or

[0043] In the formula, For line voltage fault components, For phase voltage fault components; ε PP ε is the line voltage threshold value. PG This is the phase voltage threshold value; it is set according to the voltage level, measurement device error, and reliability requirements in engineering applications.

[0044] In this embodiment of the invention, in S103, the phase-to-phase short circuit criterion is whether the negative sequence component of the short-circuit current measured by the protection is greater than or equal to the negative sequence threshold value of the phase-to-phase short-circuit fault or / and whether the zero sequence component of the short-circuit current measured by the protection is less than the zero sequence threshold value of the phase-to-phase short-circuit fault. Specifically, please refer to the following:

[0045] In the formula I2≥ε2 and I0<ε0, I2 is the negative sequence component of the short-circuit current measured by the protection, ε2 is the negative sequence threshold value of the phase-to-phase short-circuit fault, I0 is the zero sequence component of the short-circuit current measured by the protection, and ε0 is the zero sequence threshold value of the phase-to-phase short-circuit fault.

[0046] In this embodiment of the invention, the above-mentioned threshold values ​​ε PP ε PG ε1, ε2, and ε0 can be set according to the actual situation in engineering applications; this invention does not impose specific limitations on them.

[0047] In this embodiment of the invention, in S104, the fault phase selection method is to calculate the sudden change in the difference between the currents of each phase. Taking three points as an example, a fault between phases A and B is determined when the following conditions are met:

[0048]

[0049] In the formula, is the sudden change in the difference between the currents of phases BC, AB, and AC during a fault, and k is the reliability coefficient, which is chosen to be 1.5.

[0050] In this embodiment of the invention, before the phase-to-phase short circuit, the magnitude of the difference between the currents of any two phases is all The difference in current between the two faulty phases after a short circuit is greater than twice the phase current, while the current in the non-faulty phase is almost zero. Therefore, a reliability coefficient of 1.5 is chosen to ensure that the faulty phase and the non-faulty phase are correctly distinguished when a fault occurs, but the fault selection is not valid when no fault occurs.

[0051] Similarly, a fault between phases B and C is determined when the following conditions are met:

[0052]

[0053] Similarly, a fault between phases C and A is determined when the following conditions are met:

[0054]

[0055] In this embodiment of the invention, in S105, the upstream fault location k1 is calculated as follows:

[0056]

[0057] In the formula, Z s The system's equivalent impedance, The negative sequence voltage of the non-faulty phase of the busbar. Z represents the positive sequence current of the non-faulty phase at the feeder outlet. L The total impedance of the protected line. Z is the phase angle of the total impedance of the protected line. mTo measure impedance, The phase angle for measuring impedance.

[0058] When a short-circuit fault occurs between phases A and B, the measured impedance is calculated as follows:

[0059]

[0060] In the formula, U AL U BL I represents the bus voltages of phases A and B during a phase-to-phase fault. AL I BL This represents the feeder output current for phases A and B during a phase-to-phase fault.

[0061] When a short-circuit fault occurs between phases B and C, the measured impedance is calculated as follows:

[0062]

[0063] In the formula, U CL I is the bus voltage of phase C during a phase-to-phase fault. CL This is the feeder output current of phase C during a phase-to-phase fault.

[0064] When a short-circuit fault occurs between phases CA, the measured impedance is calculated as follows:

[0065]

[0066] In this embodiment of the invention, in S106, the downstream fault location k2 is calculated as follows:

[0067]

[0068] In this embodiment of the invention, in S107 and S108, the distance protection setting value k set Calculate using the following formula:

[0069]

[0070] In the formula, L p The length of the line within the protection range, L is the total length of the feeder, and k k The distance protection reliability coefficient can be set to 0.9. In this embodiment of the invention, without a distance protection reliability coefficient, the calculated results of k1 or k2 may lead to maloperation of the protection when a fault occurs in the load connected to the line. To ensure the safe and stable operation of the distribution network, a distance protection reliability coefficient of 0.9 is adopted to ensure reliable operation of the protection by limiting the protection range.

[0071] In some embodiments of the present invention, considering that the traditional distance protection reliability coefficient cannot meet the requirements of distribution networks with distributed power sources, and that the distance protection setting value is related to the line length of the protection range, this embodiment can also analyze and process the line length to obtain a more accurate distance protection reliability coefficient value.

[0072] The calculation method for the distance protection reliability coefficient includes selecting the line length L as the distance from the current protection range. p (its line segment is D) p The most recent N line segments D p-1 D p-2 ,...,D p-N ;Average of the distance protection reliability coefficients for each of the N most recent line segments These are respectively used as the initial regression values ​​Y for the corresponding line segments. p-i By minimizing the cost function This determines the allocation factor R corresponding to the line segment. p-i ; in the allocation factor R p-i Below, by changing the initial regression value Y p-i This allows us to determine the regression value under the minimum cost function. The allocation factor R for each line segment p-i The regression value under the minimum cost function of the corresponding segment The average of the products between them is used as the distance protection reliability coefficient value of the current protection range.

[0073] Where i∈[1,2,...,N], Y p-i This represents the initial regression value of the distance protection reliability coefficient for the i-th line segment that is closest to the current protection range within the line length. This represents the true value of the distance protection reliability coefficient for the i-th line segment that is closest to the current protection range within the line length. R represents the optimal regression value of the distance protection reliability coefficient for the i-th line segment closest to the current protection range. p-i The allocation factor represents the distance protection reliability coefficient of the i-th line segment that is closest to the current protection range in the line length.

[0074] In this embodiment of the invention, the structure of a distribution network containing distributed generation sources that experiences an AB phase-to-phase short-circuit fault is as follows: Figure 2As shown. The distribution network voltage level is 10kV, the system equivalent voltage is 110kV, the system equivalent impedance is 0.05 + 0.0044jΩ, and the transformer ratio is 11:1. Feeder 1 is 40km long with an impedance per unit length of 0.58-658.1jΩ / km; Feeder 2 is 20km long with the same impedance per unit length as Feeder 1. Load 1 connected to the distribution network has a capacity of 2MW and a power factor of 0.672; Load 2 has a capacity of 5MW and a power factor of 0.826; Load 3 has a capacity of 3MW and a power factor of 0.741. The distributed generation (DG) capacity is 1MW. Assuming the adaptive distance protection range is the entire length of Feeder 1, the distance protection setting value for Protection 1 is 0.9.

[0075] In this embodiment of the invention, phase-to-phase short-circuit faults are set to occur at 25%, 50%, and 75% of feeder 1, with a transition resistance of 0.1Ω. The upstream fault location parameter k1 calculated according to S105 to S106 is as follows: Figure 3 As shown, the downstream fault location parameter k2 is as follows: Figure 4 As shown. By Figure 3 and Figure 4 It can be seen that the calculated fault location is less than the distance protection setting value, indicating that the present invention can correctly judge phase-to-phase short-circuit faults under various location conditions.

[0076] In this embodiment of the invention, to verify the anti-transition resistance capability of the invention, while keeping the system parameters and fault location conditions unchanged, the transition resistance was increased to 1Ω, and the calculation results of k1 and k2 were obtained as follows: Figure 5 and Figure 6 As shown. By Figure 5 and Figure 6 It can be seen that after the transition resistance is increased, the calculated results of k1 and k2 are not significantly different from those before the transition resistance is increased. They can accurately reflect the specific location of the fault on the feeder, and thus the protection determines that a phase-to-phase short circuit fault has occurred in this line, proving that the present invention has good resistance to transition resistance.

[0077] In summary, regardless of changes in the location of the fault on the feeder, the magnitude of the transition resistance, the capacity of the distributed power supply, or the system operating mode, this invention can obtain accurate parameters reflecting the fault location on the feeder with minimal error. This allows the protection system to determine if a phase-to-phase short-circuit fault has occurred on the line, demonstrating excellent engineering adaptability and high application value. In the description of this invention, it should be understood that terms such as "coaxial," "bottom," "one end," "top," "middle," "the other end," "upper," "one side," "top," "inner," "outer," "front," "center," and "both ends" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention.

[0078] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "rotation," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0079] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An adaptive distance protection method for phase-to-phase short circuits in a distribution network containing distributed generation sources, characterized in that, The method includes the following steps: S101: Collects the voltage of the distribution network bus and the current output of each feeder; S102: Calculate the phase-to-phase voltage and the phase voltage fault component. If the phase-to-phase voltage and the phase voltage fault component meet the protection start-up criterion, execute step S103; otherwise, determine that no fault has occurred in the distribution network and execute step S101. S103: Use the negative sequence component and zero sequence component in the short-circuit current to determine whether the line fault is a phase-to-phase short-circuit fault. If it is determined that a phase-to-phase short circuit has occurred in the distribution network, execute step S104; otherwise, execute step S101. S104: Use the sudden change in the three-phase current difference during a fault to determine the faulty phase; S105: Calculate the upstream fault location using the negative sequence voltage of the non-faulty phases of the busbar and the positive sequence current of the non-faulty phases at the feeder outlet. Upstream fault location Calculate using the following method: ； In the formula, The system's equivalent impedance, The negative sequence voltage of the non-faulty phase of the busbar. This refers to the positive sequence current of the non-faulty phase at the feeder outlet. The total impedance of the protected line. The phase angle is the total impedance of the protected line. To measure impedance, The phase angle for measuring impedance; S106: Calculate the downstream fault location using the negative sequence voltage of the non-faulty phases of the busbar and the positive sequence current of the non-faulty phases at the feeder outlet. Downstream fault location Calculate using the following method: ； In the formula, The system's equivalent impedance, The negative sequence voltage of the non-faulty phase of the busbar. This refers to the positive sequence current of the non-faulty phase at the feeder outlet. The total impedance of the protected line. The phase angle is the total impedance of the protected line. To measure impedance, The phase angle for measuring impedance; S107: Compare upstream fault location With distance protection setting value ;like If yes, then execute S109; otherwise, execute S108. S108: Compare downstream fault locations With distance protection setting value ;like If the fault is found to be outside the protected area, proceed to S109; otherwise, determine that the fault is located outside the protected area and return to S101. S109: It is determined that a phase-to-phase short circuit fault has occurred within the protected area.

2. The adaptive distance protection method for phase-to-phase short circuits in a distribution network containing distributed power sources according to claim 1, characterized in that, In S102, the protection start-up criteria include determining whether the line voltage fault component is greater than the line voltage threshold or whether the phase voltage fault component is greater than the phase voltage threshold, expressed as: or ; In the formula, For line voltage fault components, This refers to the phase voltage fault component. This is the line voltage threshold value. This is the phase voltage threshold value.

3. The adaptive distance protection method for phase-to-phase short circuits in a distribution network containing distributed power sources according to claim 1, characterized in that, In S103, the phase-to-phase short-circuit criterion includes whether the negative sequence component of the short-circuit current measured by the protection is greater than or equal to the negative sequence threshold value of the phase-to-phase short-circuit fault and whether the zero sequence component of the short-circuit current measured by the protection is less than the zero sequence threshold value of the phase-to-phase short-circuit fault, expressed as: and ; In the formula, To protect the measured negative sequence component of the short-circuit current, This is the negative sequence threshold value for phase-to-phase short-circuit faults; To protect the measured zero-sequence component of the short-circuit current, This is the zero-sequence threshold value for phase-to-phase short-circuit faults.

4. The adaptive distance protection method for phase-to-phase short circuits in a distribution network containing distributed power sources according to claim 1, characterized in that, In S104, the fault phase selection method includes calculating the sudden change in the difference between the currents of each phase; a fault between phases A and B is determined when the following conditions are met: ； In the formula, , , The values ​​are, in order, the sudden changes in the differences between the currents of phases BC, AB, and AC during a fault. This is the reliability coefficient.

5. The adaptive distance protection method for phase-to-phase short circuits in a distribution network containing distributed power sources according to claim 1, characterized in that, In S105, impedance is measured. The impedance is calculated as follows when a short-circuit fault occurs between phases A and B: ； In the formula, , This refers to the bus voltages of phases A and B during a phase-to-phase fault. , This represents the feeder output current for phases A and B during a phase-to-phase fault.

6. The adaptive distance protection method for phase-to-phase short circuits in a distribution network containing distributed power sources according to claim 1, characterized in that, Distance protection setting value Calculate using the following formula: ； In the formula, The length of the line within the protection zone, For the total length of the feeder, This is the reliability coefficient for distance protection.

7. An adaptive distance protection method for phase-to-phase short circuits in a distribution network containing distributed generation sources, as described in any one of claims 1-6, characterized in that: The method also includes identifying feeders with various transition resistances and different grounding methods that experience phase-to-phase short-circuit faults; and taking protective measures for feeders that experience phase-to-phase short-circuit faults.

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