Equivalent parameter estimation method, device and equipment for power distribution line

Abstract

The application provides a power distribution line equivalent parameter estimation method, device and equipment, and relates to the technical field of power distribution networks. The method comprises the following steps: obtaining voltage and current phasors of a first end and a second end of a protected line; obtaining first and second voltage amplitudes along each point of the protected line based on the voltage and current phasors of the first end and the second end, and calculating the difference of the voltage amplitudes corresponding to each point to determine that the point corresponding to the minimum difference is a target position; determining the impedance value of an equivalent load corresponding to the target position according to an equivalent model of the protected line, the target position, the voltage and current phasors of the first end and the second end; wherein the equivalent model is constructed by star-delta transformation, and at least one unmeasurable load branch connected to the protected line is equivalent to a load connected to the protected line. The application can determine the equivalent parameters without strict synchronization of the measurement signals at both ends of the line.

Description

Technical Field

[0001] This invention relates to the field of power distribution network technology, and in particular to a method, apparatus and equipment for estimating equivalent parameters of power distribution lines. Background Technology

[0002] Distribution networks are characterized by short sections and numerous branches. If measurement and synchronization communication devices (such as those based on fiber optic and 5G communication) are installed at both ends of each section, the required equipment investment would be too large, making it difficult to meet the economic requirements of engineering practice. Therefore, in engineering projects, loads are usually allowed to operate in T-connection configurations. Some T-connected loads have "unmeasurable" characteristics, which pose challenges to the protection and control of the distribution network: on the one hand, for T-connected loads with smaller capacity, due to their lower importance, only simple protection components such as fuses are usually installed, without dedicated monitoring equipment; on the other hand, although some important T-connected loads with larger capacity are equipped with voltage and current monitoring devices, no communication link is established with both ends of the line, resulting in the inability of both ends to obtain real-time operating data of such loads. Both of these situations constitute "unmeasurable branches".

[0003] In distribution networks containing unmeasurable branches, the shunting effect of these branches can cause the power flowing into and out of the network to become unbalanced during normal operation or when a fault occurs outside the distribution area (e.g., ...). Figure 1 middle When there are unpredictable branches accessing or exiting, and In traditional current differential protection or power differential protection schemes, the lack of balance can easily lead to maloperation of the protection device. If the protection threshold is increased to avoid maloperation, the protection device may fail to operate when a fault occurs within the protected line area because the fault signal does not reach the threshold (especially in scenarios with large transition resistance and small fault current), severely affecting the reliability and sensitivity of the protection. To address these issues, existing technologies have proposed estimation methods for distribution network parameters, but these methods require extremely high synchronization of measurement data at both ends of the line. Currently, the mainstream methods for achieving data synchronization include fiber optic communication and 5G communication. While fiber optic communication can achieve high-precision synchronization, its high deployment cost makes large-scale deployment difficult. 5G communication has lower costs but inherent time delays, failing to meet strict synchronization requirements. Therefore, existing technologies struggle to balance low cost and low synchronization requirements with the requirements of protection reliability and sensitivity when addressing the problem of protection maloperation or failure to operate caused by unmeasurable branches. Summary of the Invention

[0004] This invention provides a method, apparatus, and equipment for estimating equivalent parameters of power distribution lines, in order to solve the problem that in power distribution networks with unmeasurable branches, it is difficult to balance the requirements of low cost and low synchronization with the protection reliability and sensitivity in differential protection schemes.

[0005] In a first aspect, embodiments of the present invention provide a method for estimating equivalent parameters of a power distribution line, including: Obtain the voltage phasor and current phasor of the first and second terminals of the protected line; wherein the protected line is a portion of the distribution line. Based on the voltage phasor and current phasor of the first terminal, the first voltage amplitude at each point along the protected line is obtained. Based on the voltage phasor and current phasor of the second terminal, the second voltage amplitude at each point along the protected line is obtained. The difference between the first voltage amplitude and the second voltage amplitude at each point is calculated, and the point corresponding to the minimum difference is determined as the target position. Based on the equivalent model of the protected line, the target location, and the voltage and current phasors of the first and second terminals, the impedance value of the equivalent load corresponding to the target location is determined; wherein, the equivalent model is constructed by transforming at least one unmeasurable load branch connected to the protected line by a star-delta transformation into a load connected to the protected line by a T-connection.

[0006] In one possible implementation, obtaining the first voltage amplitude at each point along the protected line based on the voltage phasor and current phasor of the first terminal, and obtaining the second voltage amplitude at each point along the protected line based on the voltage phasor and current phasor of the second terminal, includes: Substitute the voltage phasors and current phasors of the first and second terminals into the first voltage amplitude calculation formula and the second voltage amplitude calculation formula corresponding to the protected line, respectively, to calculate the first voltage amplitude and the second voltage amplitude along each point of the protected line. The first voltage amplitude calculation formula and the second voltage amplitude calculation formula include: the length of the protected line and the line impedance per unit length.

[0007] In one possible implementation, the formula for calculating the first voltage amplitude is:

[0008] The formula for calculating the second voltage amplitude is:

[0009] In the formula, The length of the protected line. Let be the distance from any point on the line to the first end. , These are the first-terminal voltage phasor and current phasor; , For the second-terminal voltage phasor and current phasor, The line impedance per unit length of the protected line.

[0010] In one possible implementation, the equivalent model is:

[0011] In the formula, The length of the protected line. The distance from the target location to the first end. , These are the first-terminal voltage phasor and current phasor; , For the second-terminal voltage phasor and current phasor, The line impedance per unit length of the protected line.

[0012] In one possible implementation, calculating the difference between the first voltage amplitude and the second voltage amplitude corresponding to each point, and determining the point corresponding to the minimum difference as the target location, includes: A difference function is constructed based on the absolute value of the difference between the first voltage amplitude and the second voltage amplitude; wherein, the difference function is:

[0013] In the formula, , These are the first voltage amplitude and the second voltage amplitude, respectively; Find the solution that minimizes the value of the difference function. The value is recorded as the target position.

[0014] In one possible implementation, obtaining the voltage phasors and current phasors of the first and second terminals of the protected line includes: Collect the voltage and current values ​​at the first and second terminals of the protected line; The positive direction is defined as the direction in which the current flows from the busbar to the protected line, and the corresponding voltage phasor and current phasor are determined based on the voltage and current values ​​of the first and second terminals.

[0015] Secondly, embodiments of the present invention provide a differential protection method for power distribution lines, comprising: Identify one or more protected lines in the power distribution network; Obtain the voltage phasor and current phasor of the first and second terminals of each protected line, and determine the equivalent parameters of each protected line according to the method in the first aspect above or any possible implementation of the first aspect. Based on the equivalent parameters of each protected line, a linkage protection criterion is constructed, and when a fault is determined to exist based on the linkage protection criterion, a corresponding differential protection scheme is formulated based on the fault location; wherein, the fault type includes intra-zone faults and extra-zone faults.

[0016] One possible implementation also includes: When a target protected line experiences a fault within the affected area, the voltage phasors and current phasors of the first and second terminals of the target protected line are reacquired, and the equivalent parameters corresponding to the target protected line are redefined.

[0017] Thirdly, embodiments of the present invention provide a differential protection device for power distribution lines, comprising: The route determination module is used to determine one or more protected lines in the distribution network. The power distribution line equivalent parameter estimation module is used to obtain the voltage phasor and current phasor of the first and second terminals of each protected line, and to determine the equivalent parameters of each protected line according to the method in the first aspect above or any possible implementation of the first aspect. The differential protection module is used to construct linkage protection criteria based on the equivalent parameters of each protected line, and to formulate a corresponding differential protection scheme based on the fault location when a fault is determined to exist based on the linkage protection criteria; wherein, the fault type includes intra-zone faults and inter-zone faults.

[0018] Fourthly, embodiments of the present invention provide an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the method described in the first aspect or any possible implementation thereof.

[0019] In this embodiment of the invention, by acquiring the voltage phasors and current phasors of the first and second ends of the protected line, and using star-delta transformation, multiple T-connected unmeasurable load branches on the protected line are equivalent to a single T-connected load, an equivalent model that fits the actual line topology is constructed. Then, the first voltage amplitude and second voltage amplitude of each point on the line corresponding to the voltage phasors and current phasors at both ends are calculated respectively. Based on the amplitude difference at each point, the target position corresponding to the minimum difference is locked. Finally, the impedance value of the equivalent load is determined by combining the equivalent model and the measured data. This not only accurately quantifies the shunting effect of unmeasurable load branches, but also eliminates the need for strict synchronization of measurement signals at both ends of the line. This effectively solves the problem of false tripping or failure to trip caused by the existence of unmeasurable branches in traditional protection schemes, while reducing the performance requirements of the communication system and improving the accuracy of subsequent differential protection of distribution lines. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of an equivalent model of a power distribution line provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of an equivalent model of a power distribution line provided in another embodiment of the present invention; Figure 3 This is an equivalent T-type power distribution line topology provided in one embodiment of the present invention; Figure 4a and Figure 4b These are the equivalent network electrical phasor characteristics provided by embodiments of the present invention under different scenarios; Figure 5 This is a flowchart illustrating a method for estimating equivalent parameters of power distribution lines according to an embodiment of the present invention. Figure 6 This is a flowchart illustrating a differential protection method for power distribution lines according to an embodiment of the present invention. Figure 7 This is a schematic diagram of an equivalent model of a power distribution line provided in another embodiment of the present invention; Figure 8a and 8b yes Figure 7 A schematic diagram showing the difference between the estimated power and the measured power under different conditions in the power distribution line shown. Figure 9 This is a schematic diagram of the structure of a differential protection device for power distribution lines provided in an embodiment of the present invention; Figure 10 This is a schematic diagram of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0021] Before introducing the method for estimating the equivalent parameters of power distribution lines provided in the embodiments of this application, the principle of equivalent network transformation for unmeasurable branches of T-connections will be introduced first.

[0022] like Figure 2 This is a schematic diagram of an equivalent model of a power distribution line according to an embodiment of this application. Figure 2 The distribution line mn contains three unmeasurable branches connected by T-junctions. First, a star-delta equivalent transformation is performed on the structure within the red box. The impedance relationships after the transformation are as follows:

[0023]

[0024] in, The impedance of the line within the red box is... , All are load impedances within the red box. , , All are impedances after equivalent transformation. Because the distribution network satisfies... << , << The above formula can be simplified to:

[0025]

[0026] Therefore, the line impedance remains essentially unchanged before and after the equivalent transformation, and the equivalent load impedance is approximately equal to the parallel connection of the two loads before the equivalent transformation. Based on this, the topology of the distribution line is further simplified through equivalence, ultimately yielding... Figure 3 The equivalent T-type power distribution line topology shown is illustrated.

[0027] Based on the above equivalent process, Figure 1 After equivalence of all unmeasurable branches, the distance between the grid connection location of the equivalent load and the m-end of the line. It depends on the distribution of unmeasurable load branches on the protected line. Equivalent distribution network line parameters. , With load parameters The following relationship must be satisfied:

[0028]

[0029] During normal operation or in the event of an external fault (i.e., such as...) Figure 1 middle When a fault occurs outside the distribution line mn, the internal topology and impedance parameters of the distribution line mn are relatively stable, and the distance between the equivalent load grid connection point and the m end is... Equivalent load parameters Basically unchanged. Faults occur within the affected area (i.e., such as...). Figure 1 middle When a fault occurs within the distribution line (mn), the internal structure of the distribution line changes. At this time, by accurately estimating the equivalent network parameters, the impact of unmeasurable load branches on the protection can be quantified. Based on the changing characteristics of the protected line's structure and parameters, a longitudinal protection criterion can be dynamically constructed, which can effectively solve the problem of reduced reliability and sensitivity of traditional protection after unmeasurable load branches are connected to the grid.

[0030] After introducing the principle of equivalent network transformation for unmeasurable branches, the principle of equivalent network parameter estimation will be introduced below.

[0031] like Figure 1 As shown, the busbar typically points towards the protected line (i.e., Figure 1 If the distribution line (mn) is taken as the positive direction, then for the m end, The direction indicated is the positive direction, referring to the n-end. The indicated direction is the positive direction. After distributed generation (DG) is connected to the grid, it will affect the power flow direction of the traditional power distribution system. Specifically, when the downstream of the protected line is heavily loaded and the DG output is relatively small, the bus side supplies power to the downstream of the protected line. The power flow direction at the n-end of the distribution line will then be different from its corresponding positive direction (i.e.,...). Conversely, when the downstream of the protected line is lightly loaded and the output of the distribution generator (DG) is large, the DG may supply power to the protected line. In this case, the power flow direction at the n end of the distribution line will be the same as the positive direction.

[0032] For the two scenarios mentioned above, Figure 1 Equivalent processing of protection lines to obtain such Figure 3 After showing the equivalent T-type power distribution line topology diagram, the relationships between the electrical quantities in the topology are as follows: Figure 4a and Figure 4b As shown, Figure 4a and Figure 4b In the diagram, the shaded area between the red dashed line and the black solid line represents the deviation between the voltage amplitude at each point on the line calculated solely from the electrical quantities at terminals m or n, assuming the shunting effect of the equivalent load is ignored. Figure 4a and Figure 4b middle The voltage phasor measured at the m-end of the busbar is denoted as . The current phasor measured at the m-end of the busbar is... The voltage phasor measured at the n-terminal of the busbar. The current phasor measured at the n-end of the busbar. for Figure 3 Medium-efficiency load The equivalent voltage phasor at both ends. This represents the voltage phasor measured at the m-end of the bus. With current phasor phase difference, This represents the impedance angle of the equivalent load. (From...) Figure 4a and 4b It can be seen that if the voltage amplitude at each point on the line is estimated using the local voltage and current information at the m and n ends of the line, the location where the voltage estimates differ the least is the location where the equivalent load is connected. Therefore, the estimation method for relevant parameters of the equivalent load is established as follows: Using the voltage and current data measured independently at terminals m and n of the line, estimate the voltage amplitude at each point on the line:

[0033]

[0034] In the formula, The length of the protected line. Let m be the distance from any point on the line to end m. , and , The voltage and current phasors at the m and n ends of the line are measured respectively. The impedance per unit length of the line. , These are estimated values ​​for calculating the voltage amplitude at each point on the line using information from the m and n terminals respectively.

[0035] On the protected line, the difference in voltage amplitude calculated from the electrical quantities measured on both sides can be expressed as:

[0036] In the formula, This is a difference function. During normal operation, when... When the minimum value is obtained, the value of the corresponding independent variable is... This is the distance between the equivalent load grid connection location and the m-end of the line.

[0037] Combination Figure 3 Based on the topological characteristics, the following relationship is further obtained:

[0038] After simplification, the estimated equivalent load impedance is:

[0039] Based on the above introduction of the equivalent principle, this application provides a method for estimating the equivalent parameters of a power distribution line. First, the voltage amplitude at each point on the line is calculated using the voltage and current phasors measured independently at the m and n ends of the line. Second, based on the difference function... The minimum value determines the equivalent load grid connection location; finally, combined with Figure 3 Using the T-shaped topology and distribution network parameters shown, the equivalent load impedance is estimated. Notably, this method does not require strict synchronization of sampling signals on both sides of the line, reducing the requirements for the communication system.

[0040] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0041] Figure 5 This diagram illustrates an application scenario of the power distribution line equivalent parameter estimation method provided in this embodiment of the invention. Figure 6 As shown, S501, obtain the voltage phasor and current phasor of the first and second terminals of the protected line; wherein, the protected line is a part of the distribution line.

[0042] The execution subject of each embodiment of this application can be a server, processor, microprocessor, or other device with data processing capabilities. In actual implementation, the specific implementation method of the execution subject can be selected according to actual needs. This embodiment does not impose any particular restrictions on this, as long as it is a device with data processing capabilities.

[0043] In practice, power distribution lines cover a wide area. To reduce the construction cost of measurement and synchronization communication devices and improve the accuracy of key protection, a portion of the line is often selected as the protected line. For example, for power distribution lines longer than 15km, distinguishing them from peripheral or rural areas, a 3km section within the 15km radius containing loads supplying key enterprises is selected as the protected line. In this case, installing measurement and synchronization communication devices only within this 3km section can reduce costs.

[0044] S502: Based on the voltage phasor and current phasor of the first terminal, obtain the first voltage amplitude at each point along the protected line; based on the voltage phasor and current phasor of the second terminal, obtain the second voltage amplitude at each point along the protected line; calculate the difference between the first voltage amplitude and the second voltage amplitude at each point; and determine the point corresponding to the minimum difference as the target position.

[0045] The core of traditional differential protection is based on phasor operations, such as the phase difference of current phasors and the superposition of power phasors. The accuracy of phasors directly depends on the time synchronization of the measurement signals at both ends. For example, traditional solutions require high-precision synchronization methods such as optical fibers to ensure that the current and voltage signals collected at both ends are aligned on the same time scale. If 5G communication is used, there will be a time delay, and the phase difference will deviate, leading to errors in the calculation of inflow and outflow power, which in turn will cause the protection to malfunction or fail to operate.

[0046] Based on the aforementioned introduction to the principle of equivalent network parameter estimation, the core of equivalent parameter estimation is to "obtain the estimated value of the voltage amplitude at each point on the line by independently measuring the voltage and current data at both ends of the line", and to determine the location of the equivalent load based on "minimum difference in voltage amplitude between the two ends".

[0047] In this method, voltage amplitude is a scalar quantity that only reflects the magnitude of the voltage and is independent of phase. Traditional methods rely on voltage and current phasors, which include both magnitude and phase. Phase is extremely sensitive to time synchronization; even a microsecond delay can cause phase deviation. In this application, voltage amplitude measurement only requires accurate local acquisition and does not require attention to the time alignment of signals at both ends. As long as each end can accurately measure its own voltage and current magnitude, the voltage amplitude at each point on the line can be independently calculated. The calculation of the amplitude difference between the two ends is not affected by "time asynchrony".

[0048] In one possible implementation, a first voltage amplitude at each point along the protected line is obtained based on the voltage phasor and current phasor at the first terminal, and a second voltage amplitude at each point along the protected line is obtained based on the voltage phasor and current phasor at the second terminal, including: Substitute the voltage phasors and current phasors of the first and second terminals into the first voltage amplitude calculation formula and the second voltage amplitude calculation formula of the corresponding protected line, respectively, to calculate the first voltage amplitude and the second voltage amplitude at each point along the protected line. The first voltage amplitude calculation formula and the second voltage amplitude calculation formula include: the length of the protected line and the line impedance per unit length.

[0049] In conjunction with the foregoing embodiments Figure 4a , Figure 4b The introduction to the principle of equivalent network parameter estimation, and the formula for calculating the first voltage amplitude are:

[0050] The formula for calculating the second voltage amplitude is:

[0051] In the formula, The length of the protected line, Let be the distance from any point on the line to the first end. , These are the first-terminal voltage phasor and current phasor; , For the second-terminal voltage phasor and current phasor, The line impedance per unit length of the protected line.

[0052] S503, based on the equivalent model of the protected line, the target location, and the voltage and current phasors of the first and second terminals, determine the impedance value of the equivalent load corresponding to the target location; wherein, the equivalent model is constructed by transforming at least one unmeasurable load branch connected to the protected line by a star-delta connection into a load connected to the protected line by a star-delta connection.

[0053] In conjunction with the foregoing embodiments Figure 2 , Figure 3 This includes an introduction to the principle of equivalent network transformation, calculating the difference between the first and second voltage amplitudes at each point, and determining the point corresponding to the minimum difference as the target location, including: A difference function is constructed based on the absolute value of the difference between the first voltage amplitude and the second voltage amplitude; where the difference function is:

[0054] In the formula, , These are the first voltage amplitude and the second voltage amplitude, respectively; Find the solution that minimizes the difference function. The value is recorded as the target position.

[0055] The equivalent model is:

[0056] In the formula, The length of the protected line, The distance from the target location to the first end. , These are the first-terminal voltage phasor and current phasor; , For the second-terminal voltage phasor and current phasor, The line impedance per unit length of the protected line.

[0057] In this embodiment, by acquiring the voltage phasors and current phasors of the first and second ends of the protected line, and using star-delta transformation, multiple T-connected unmeasurable load branches on the protected line are equivalent to a single T-connected load, an equivalent model that fits the actual line topology is constructed. Then, the first voltage amplitude and second voltage amplitude of each point on the line corresponding to the voltage phasors and current phasors at both ends are calculated respectively. Based on the amplitude difference at each point, the target position corresponding to the minimum difference is locked. Finally, the impedance value of the equivalent load is determined by combining the equivalent model and the measured data. This not only accurately quantifies the shunting effect of unmeasurable load branches, but also eliminates the need for strict synchronization of measurement signals at both ends of the line. This effectively solves the problem of false tripping or failure to trip caused by the existence of unmeasurable branches in traditional protection schemes, while reducing the performance requirements of the communication system and improving the accuracy of subsequent differential protection of distribution lines.

[0058] In one possible implementation, obtaining the voltage phasors and current phasors at the first and second terminals of the protected line includes: Collect the voltage and current values ​​at the first and second terminals of the protected line; The positive direction is defined as the direction in which the current flows from the busbar to the protected line, and the corresponding voltage phasor and current phasor are determined based on the voltage and current values ​​of the first and second terminals.

[0059] In this embodiment, the process of acquiring voltage and current phasors at both ends of the protected line first standardizes the acquisition of voltage and current values ​​at the first and second ends, and then uniformly uses the direction of current flow from the bus to the protected line as the positive direction to determine voltage and current phasors. This establishes a unified data acquisition standard and phasor direction reference, effectively ensuring the consistency and comparability of measurement data at both ends, avoiding basic data deviations caused by inconsistent acquisition methods or confusing direction definitions, and improving the accuracy of voltage amplitude calculation, difference analysis, and equivalent parameter estimation.

[0060] This invention also provides a differential protection method for power distribution lines, comprising: S601, identify one or more protected lines in the distribution network.

[0061] As described in the aforementioned embodiments, for distribution network lines with a wide coverage area, key load lines can be selected as protected lines. When multiple key loads are included, multiple protected lines can be divided for focused attention. The equivalent parameter estimation method provided in the aforementioned embodiments can be used to obtain the equivalent parameters of each protected line, so as to improve the accuracy of differential protection and ensure the safe and stable operation of the power grid.

[0062] S602, obtain the voltage phasor and current phasor of the first and second terminals of each protected line, and determine the equivalent parameters of each protected line according to the power distribution line equivalent parameter estimation method provided in any of the foregoing embodiments.

[0063] S603 constructs linkage protection criteria based on the equivalent parameters of each protected line, and formulates corresponding differential protection schemes based on the fault location when a fault is determined to exist based on the linkage protection criteria; the fault types include intra-zone faults and extra-zone faults.

[0064] In this embodiment, by first identifying one or more protected lines in the distribution network, and then using the aforementioned equivalent parameter estimation method to obtain the accurate equivalent parameters of each protected line, a linkage protection criterion that fits the actual operating scenario is constructed based on these equivalent parameters. This can accurately distinguish between faults within and outside the zone, and formulate appropriate differential protection schemes for different fault locations. This not only effectively solves the problem of false tripping or failure to trip caused by the unmeasurable load branch diversion of traditional differential protection, but also eliminates the need for high-cost synchronization communication equipment by relying on parameter estimation methods with low synchronization requirements. While ensuring the sensitivity and reliability of protection actions, it also takes into account the economy of engineering applications, significantly improving the overall operating performance of the distribution network protection system.

[0065] One possible implementation also includes: When a target protected line experiences a fault within the affected area, the voltage phasors and current phasors of the first and second terminals of the target protected line are reacquired, and the equivalent parameters corresponding to the target protected line are redefined.

[0066] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0067] To verify the reliability of the solution provided in this application, a 10kV power distribution system simulation model as shown in the figure below was built on the PSCAD / EMTDC simulation platform. The transformer equivalent impedance is j0.34Ω, and the line impedance is 0.17+j0.34Ω / km. The calculations under normal operation are as follows: Figure 4a and 4bThe network equivalent parameters are shown. Different transition resistance faults are set outside the region. According to... Figure 7 The equivalent network uses voltage and current information on one side to deduce power information on the other side. If the difference between the deduced information and the measured information is 0, then the method has a good equivalent effect.

[0068] The difference between the estimated power and the measured power is as follows: Figure 8a and 8b As shown. The calculation results indicate that after an external fault occurs on the line, and The calculated power on both sides is basically consistent with the measured power. The equivalent effect is good, and this equivalent method only uses the voltage amplitude and voltage-current phasor ratio information, so the requirement for information synchronization is low.

[0069] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0070] Figure 9 A schematic diagram of the equivalent parameter estimation device for power distribution lines provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below: like Figure 9 As shown, the power distribution line equivalent parameter estimation device 9 includes: Route determination module 901 is used to determine one or more protected lines in the distribution network; The power distribution line equivalent parameter estimation module 902 is used to obtain the voltage phasor and current phasor of the first and second terminals of each protected line, and to determine the equivalent parameters of each protected line according to the power distribution line equivalent parameter estimation method provided in any of the above embodiments. The differential protection module 903 is used to construct linkage protection criteria based on the equivalent parameters of each protected line, and to formulate a corresponding differential protection scheme based on the fault location when a fault is determined to exist based on the linkage protection criteria; the fault types include intra-zone faults and inter-zone faults.

[0071] The equivalent parameter estimation module 902 for power distribution lines is specifically used for: Obtain the voltage phasor and current phasor of the first and second terminals of the protected line; wherein the protected line is a part of the distribution line. Based on the voltage phasor and current phasor at the first end, the first voltage amplitude at each point along the protected line is obtained. Based on the voltage phasor and current phasor at the second end, the second voltage amplitude at each point along the protected line is obtained. The difference between the first voltage amplitude and the second voltage amplitude at each point is calculated, and the point corresponding to the minimum difference is determined as the target position. Based on the equivalent model of the protected line, the target location, and the voltage and current phasors of the first and second terminals, the impedance value of the equivalent load corresponding to the target location is determined. The equivalent model is constructed by transforming at least one unmeasurable load branch connected to the protected line by a star-delta connection into a load connected to the protected line by a star-delta connection.

[0072] In one possible implementation, the power distribution line equivalent parameter estimation module 902 is specifically used for: Substitute the voltage phasors and current phasors of the first and second terminals into the calculation formulas for the first and second voltage amplitudes of the corresponding protected lines, respectively, to calculate the first voltage amplitude and second voltage amplitude at each point along the protected line. The first voltage amplitude calculation formula and the second voltage amplitude calculation formula include: the length of the protected line and the line impedance per unit length.

[0073] In one possible implementation, the power distribution line equivalent parameter estimation module 902 is specifically used for: A difference function is constructed based on the absolute value of the difference between the first voltage amplitude and the second voltage amplitude; where the difference function is:

[0074] In the formula, , These are the first voltage amplitude and the second voltage amplitude, respectively; Find the solution that minimizes the difference function. The value is recorded as the target position.

[0075] In one possible implementation, the power distribution line equivalent parameter estimation module 902 is specifically used for: Collect the voltage and current values ​​at the first and second terminals of the protected line; The positive direction is defined as the direction in which the current flows from the busbar to the protected line, and the corresponding voltage phasor and current phasor are determined based on the voltage and current values ​​of the first and second terminals.

[0076] In this embodiment, by first identifying one or more protected lines in the distribution network, and then using the aforementioned equivalent parameter estimation method to obtain the accurate equivalent parameters of each protected line, a linkage protection criterion that fits the actual operating scenario is constructed based on these equivalent parameters. This can accurately distinguish between faults within and outside the zone, and formulate appropriate differential protection schemes for different fault locations. This not only effectively solves the problem of false tripping or failure to trip caused by the unmeasurable load branch diversion of traditional differential protection, but also eliminates the need for high-cost synchronization communication equipment by relying on parameter estimation methods with low synchronization requirements. While ensuring the sensitivity and reliability of protection actions, it also takes into account the economy of engineering applications, significantly improving the overall operating performance of the distribution network protection system.

[0077] Figure 10 This is a schematic diagram of an electronic device provided in an embodiment of the present invention. Figure 10 As shown, the electronic device 10 of this embodiment includes a processor 100 and a memory 101. The memory 101 stores a computer program 102. When the processor 100 executes the computer program 102, it implements the steps in the various method embodiments described above. Alternatively, when the processor 100 executes the computer program 102, it implements the functions of each module / unit in the various device embodiments described above.

[0078] For example, computer program 102 may be divided into one or more modules / units, which are stored in memory 101 and executed by processor 100 to complete the present invention. The one or more modules / units may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of computer program 102 in electronic device 10.

[0079] Electronic device 10 may include, but is not limited to, processor 100 and memory 101. Those skilled in the art will understand that... Figure 10 This is merely an example of electronic device 10 and does not constitute a limitation on electronic device 10. It may include more or fewer components than shown, or combine certain components, or different components. For example, electronic device 10 may also include input / output devices, network access devices, buses, etc.

[0080] For the sake of simplicity and clarity, only the above-described functional modules / units are used as examples. In practical applications, the functions described above can be assigned to different functional modules / units as needed. These modules / units can be implemented in hardware, software, or a combination of both.

[0081] In the above embodiments, the descriptions of each embodiment have their own emphasis. Parts not detailed or described in a particular embodiment can be referred to in the relevant descriptions of other embodiments. Unless otherwise specified or in conflict with logic, the terminology and / or descriptions between different embodiments are consistent and can be referenced interchangeably. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships.

[0082] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for estimating equivalent parameters of a power distribution line, characterized in that, include: Obtain the voltage phasors and current phasors of the first and second ends of the protected line; wherein the protected line is a portion of a distribution line; based on the voltage phasors and current phasors of the first end, obtain the first voltage amplitude at each point along the protected line, and based on the voltage phasors and current phasors of the second end, obtain the second voltage amplitude at each point along the protected line, and calculate the difference between the first voltage amplitude and the second voltage amplitude at each point, determining the point corresponding to the minimum difference as the target location; based on the equivalent model of the protected line, the target location, and the voltage phasors and current phasors of the first and second ends, determine the impedance value of the equivalent load corresponding to the target location; wherein the equivalent model is constructed by transforming at least one T-connected unmeasurable load branch on the protected line into a T-connected load on the protected line through star-delta transformation.

2. The method for estimating equivalent parameters of power distribution lines according to claim 1, characterized in that, The step of obtaining a first voltage amplitude at each point along the protected line based on the voltage phasor and current phasor of the first terminal, and obtaining a second voltage amplitude at each point along the protected line based on the voltage phasor and current phasor of the second terminal, includes: Substitute the voltage phasors and current phasors of the first and second terminals into the first voltage amplitude calculation formula and the second voltage amplitude calculation formula corresponding to the protected line, respectively, to calculate the first voltage amplitude and the second voltage amplitude along each point of the protected line. The first voltage amplitude calculation formula and the second voltage amplitude calculation formula include: the length of the protected line and the line impedance per unit length.

3. The method for estimating equivalent parameters of power distribution lines according to claim 2, characterized in that, The formula for calculating the first voltage amplitude is: The formula for calculating the second voltage amplitude is: In the formula, The length of the protected line. Let be the distance from any point on the line to the first end. , The first terminal voltage phasor and current phasor; , For the second-terminal voltage phasor and current phasor, The line impedance per unit length of the protected line.

4. The method for estimating equivalent parameters of power distribution lines according to claim 3, characterized in that, The equivalent model is: In the formula, The length of the protected line. The distance from the target location to the first end. , The first terminal voltage phasor and current phasor; , For the second-terminal voltage phasor and current phasor, The line impedance per unit length of the protected line.

5. The method for estimating equivalent parameters of power distribution lines according to claim 3, characterized in that, The step of calculating the difference between the first voltage amplitude and the second voltage amplitude at each point, and determining the point corresponding to the minimum difference as the target location, includes: A difference function is constructed based on the absolute value of the difference between the first voltage amplitude and the second voltage amplitude; wherein, the difference function is: In the formula, , These are the first voltage amplitude and the second voltage amplitude, respectively; Find the solution that minimizes the value of the difference function. The value is recorded as the target position.

6. The method for estimating equivalent parameters of power distribution lines according to claim 1, characterized in that, The acquisition of the voltage phasors and current phasors at the first and second terminals of the protected line includes: Collect the voltage and current values ​​at the first and second terminals of the protected line; The positive direction is defined as the direction in which the current flows from the busbar to the protected line, and the corresponding voltage phasor and current phasor are determined based on the voltage and current values ​​of the first and second terminals.

7. A differential protection method for power distribution lines, characterized in that, include: Identify one or more protected lines in the power distribution network; Obtain the voltage phasor and current phasor of the first and second terminals of each protected line, and determine the equivalent parameters of each protected line according to the power distribution line equivalent parameter estimation method according to any one of claims 1 to 6. Based on the equivalent parameters of each protected line, a linkage protection criterion is constructed, and when a fault is determined to exist based on the linkage protection criterion, a corresponding differential protection scheme is formulated based on the fault location; wherein, the fault type includes intra-zone faults and extra-zone faults.

8. The differential protection method for power distribution lines according to claim 7, characterized in that, Also includes: When a target protected line is found to have a fault within the affected area, the voltage phasors and current phasors of the first and second terminals of the target protected line are reacquired, and the equivalent parameters corresponding to the target protected line are redefined.

9. A differential protection device for power distribution lines, characterized in that, include: The route determination module is used to determine one or more protected lines in the distribution network. The power distribution line equivalent parameter estimation module is used to obtain the voltage phasor and current phasor of the first and second terminals of each protected line, and to determine the equivalent parameters of each protected line according to the power distribution line equivalent parameter estimation method according to any one of claims 1 to 8. The differential protection module is used to construct linkage protection criteria based on the equivalent parameters of each protected line, and to formulate a corresponding differential protection scheme based on the fault location when a fault is determined to exist based on the linkage protection criteria; wherein, the fault type includes intra-zone faults and inter-zone faults.

10. An electronic device, characterized in that, It includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the method as described in any one of claims 1 to 8.

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