A method and system for measuring the length of a power line

Abstract

A method and system for measuring the length of a power line is disclosed. The method includes: applying reactive power compensation to the end of each phase of the line under test, such that the power factor at the end of each phase is greater than or equal to a preset first threshold; selecting N time points at equal intervals; at each time point, determining the power loss of the phase line based on the active power at both ends of the phase line, and determining the effective current value of the phase line based on the effective current value at the beginning and / or end of the phase line; for each phase line, determining the loss resistance of the phase line by performing data fitting between the line loss power and the effective current value at the N time points; determining the length of the phase line based on the loss resistance and the resistance value per unit length; and calculating the average length of the three phase lines as the length of the line under test. By applying reactive power compensation to achieve high power factor operation and by using data fitting at multiple time points, the length of the distribution line can be accurately measured under normal operating conditions.

Description

Technical Field

[0001] This application relates to the field of power distribution line technology, specifically to a method and system for measuring the length of power lines. Background Technology

[0002] The accuracy of overhead line parameters in distribution networks is a crucial foundation for achieving intelligent power grid management and high-reliability power supply. Among these parameters, line length is not only a core data point for power grid record management and upgrade design, but also a key parameter directly determining the performance of modern traveling wave fault location technologies. Inaccurate line length data will lead to systematic deviations in fault location, severely delaying fault inspection and repair, and impacting power supply reliability.

[0003] However, in the current operation and management of power distribution networks, the accurate acquisition and dynamic maintenance of line lengths have long faced severe challenges. Effective means of monitoring the entire lifecycle length of lines are generally lacking. The line lengths recorded in the ledgers are mostly derived from measurements or rough estimates taken before commissioning. After long-term operation, deviations occur due to factors such as sag changes and line modifications, but these deviations cannot be corrected in a timely manner, resulting in discrepancies between the actual line lengths and the ledger records.

[0004] Existing methods for determining line length have significant limitations. Manual measurement and laser ranging require manual operation or maintenance along the line when power is off, making manual work impossible on operating lines and resulting in low efficiency. Geographically based methods calculate straight-line distances using tower coordinates and correct for sag, but their accuracy is affected by the accuracy of the correction model and tower coordinates. Traveling wave ranging heavily relies on high-precision time synchronization and accurate wavefront calibration, and is dependent on fault triggering and the opening and closing of line switches, making it difficult to cover the entire line and failing to meet the needs of routine active monitoring and measurement accuracy requirements. Summary of the Invention

[0005] This application provides a method and system for measuring the length of power lines, which can solve the problem in the prior art that it is impossible to actively perform high-precision length measurement of operating power distribution lines.

[0006] In a first aspect, embodiments of this application provide a method for measuring the length of a power line, including:

[0007] Reactive power compensation is applied to the end of each phase of the line under test so that the power factor at the end of each phase is greater than or equal to a preset first threshold. The line under test is a three-phase line.

[0008] N time points are selected at equal intervals, where N > 1; at each time point, the power loss of the phase line is determined based on the active power at both ends of each phase line, and the effective value of the current of the phase line is determined based on the effective value of the current at the beginning and / or end of each phase line.

[0009] For each phase of the line, the loss resistance of that phase is determined by fitting the line loss power and the effective value of the line current at N time points; the length of that phase is determined based on the loss resistance and the resistance value per unit length.

[0010] The average length of the three-phase line is calculated as the length of the line to be tested.

[0011] Furthermore, in one embodiment, the power line includes multiple segments of the line to be tested, each segment being a straight line without branches.

[0012] Furthermore, in one embodiment, the line loss power of each phase line is the difference between the active power at the beginning and the active power at the end of each phase line.

[0013] Furthermore, in one embodiment, the effective value of the line current of each phase line is the root mean square of the effective value of the current at the beginning and the effective value of the current at the end of each phase line.

[0014] Furthermore, in one embodiment, the step of determining the loss resistance of each phase line by performing data fitting using the line loss power and the effective value of the line current at N time points includes:

[0015] Calculate the square of the effective value of the line current at each time point for each phase;

[0016] Using the square of the effective value of the line current as the independent variable and the corresponding line loss power as the dependent variable, a linear regression analysis is performed on the line loss power and the square of the effective value of the line current at the N time points to obtain the regression equation.

[0017] The slope of the regression equation is taken as the loss resistance of the phase line.

[0018] Furthermore, in one embodiment, the coefficient of determination between the line loss power and the square of the effective value of the line current at the N time points is calculated. If the coefficient of determination is less than or equal to a preset second threshold, the measurement is determined to be invalid, and N time points are reselected for measurement starting from the current time.

[0019] Furthermore, in one embodiment, for each phase line, the resistance value per unit length of the phase line is determined based on the current temperature of the phase line, the temperature coefficient of resistance, and the standard resistance value per unit length.

[0020] Furthermore, in one embodiment, the measurement method is performed during a period when the line load changes gradually.

[0021] Secondly, embodiments of this application provide a power line length measurement system, comprising:

[0022] The first measuring device is configured at the beginning of the line under test to obtain the active power and effective current values ​​of each phase at the beginning of the line at each time point.

[0023] The second measuring device is located at the end of the line under test and is used to obtain the active power and effective current values ​​at the end of each phase of the line at each time point.

[0024] A reactive power compensation device, configured at the end of the line under test, is used to apply reactive power compensation to the end of each phase of the line under test, so that the power factor at the end of each phase is greater than or equal to a preset first threshold. The line under test is a three-phase line. It is also used to sequentially select N time points at equal intervals, where N > 1; at each time point, the power loss of that phase is determined based on the active power at both ends of that phase, and the effective current value of that phase is determined based on the effective current value at the beginning and / or end of that phase; for each phase, the power loss and the effective current value at the N time points are fitted to determine the power loss resistance of that phase; the length of that phase is determined based on the power loss and the resistance per unit length; and the average length of the three-phase line is calculated as the length of the line under test.

[0025] Furthermore, in one embodiment, the second measuring device is an independent measuring device, or it is integrated with the reactive power compensation device.

[0026] The beneficial effects of the technical solutions provided in this application include:

[0027] By applying reactive power compensation to the end of each phase of the circuit under test, the power factor is raised to above a preset first threshold. Multiple time points are selected sequentially. At each time point, the power loss of that phase is determined based on the active power at the beginning and end of each phase, and the effective current value of that phase is determined by combining the effective current values ​​at the beginning and end of each phase. For each phase, the power loss resistance is determined by data fitting using the power loss and effective current values ​​at all time points. The length of that phase is calculated by combining the resistance per unit length of that phase. The average length of the three phases in the circuit under test is taken as the length of the circuit under test. This method achieves high power factor operation by applying reactive power compensation to the end of each phase, ensuring the accuracy of the basic measurement data. Furthermore, the multi-time-point data fitting effectively suppresses random interference, enabling accurate measurement of the power loss resistance and length of the distribution line under normal operating conditions. This solves the problem in existing technologies where high-precision length measurement of operating distribution lines cannot be actively performed. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the power line length measurement method according to an embodiment of this application;

[0029] Figure 2This is a schematic diagram of the distribution network topology according to an embodiment of this application;

[0030] Figure 3 This is a schematic diagram of the power line length measurement system according to an embodiment of this application;

[0031] Figure 4 This is a schematic diagram of the reactive power compensation device in an embodiment of this application. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0034] In a first aspect, embodiments of this application provide a method for measuring the length of a power line.

[0035] In one embodiment, reference is made to Figure 1 , Figure 1 This is a flowchart illustrating the method for measuring the length of power lines. Figure 1 As shown, the measurement method includes:

[0036] S1. The line under test is a three-phase line. Reactive power compensation is applied to the end of each phase of the line under test so that the power factor of the end of each phase is greater than or equal to the preset first threshold.

[0037] S2. Select N time points at equal intervals, where N>1; at each time point, determine the power loss of the phase line based on the active power at both ends of each phase line, and determine the effective value of the current of the phase line based on the effective value of the current at the beginning and / or end of each phase line.

[0038] S3. For each phase of the line, the loss resistance of that phase is determined by fitting the line loss power and the effective value of the line current at N time points; based on the above loss resistance and the resistance value per unit length, the length of that phase is determined.

[0039] S4. Calculate the average length of the three-phase line as the length of the line to be tested.

[0040] Furthermore, the aforementioned power lines include multiple sections of the line to be tested, each of which is a straight section without branches.

[0041] In S1 above, the preset first threshold is set empirically based on the following: when the power factor is greater than or equal to the preset first threshold, the reactive power at the end of the line has been reduced to a sufficiently low level, significantly weakening the impact of reactive power fluctuations on measurement stability, while ensuring the economy and feasibility of the compensation device. In this embodiment, the first threshold is set to 0.95.

[0042] Before reactive power compensation, the reactive power at the end of each phase of the line under test is characterized by large values ​​and drastic instantaneous changes, especially when the distribution network is connected to industrial loads. These reactive power variations cause large and rapid fluctuations in the reactive power flow of each phase, severely interfering with the measurement of the actual loss status of each phase. Simultaneously, due to the low power factor, there is a significant phase difference between the voltage and current at the end of each phase, i.e., a large phase angle φ. The calculation of the active power P at the end of each phase is shown in equation (1):

[0043] (1)

[0044] Where U is the effective value of the voltage at the end of the phase line, I is the effective value of the current at the end of the phase line, and φ is the phase angle between the voltage and current at the end of the phase line.

[0045] In this state, the active power P is extremely sensitive to the measurement error of the phase angle φ: when the phase angle φ is large, cosφ is extremely sensitive to small changes in φ, and a small phase measurement deviation will lead to a huge error in the calculated value of active power.

[0046] After reactive power compensation, the power factor at the end of each phase of the line under test is raised to a high level close to 1, making the reactive power at the end of each phase approach zero. The total current of each phase is approximately equal to the active current, and its fluctuation is approximately linearly related to the fluctuation of the active power. At this time, the reactive power itself is very small and stable, and the measured value of the active power becomes stable. When used for line loss calculation, even if the average value of a longer time scale is used, its representative error is extremely small. The power factor is constant at a high level, which greatly simplifies the calculation model of line loss, eliminates the calculation error caused by inaccurate reactive power values, and improves the overall reliability of the calculation. At the same time, since the voltage and current phases at the end of each phase are almost the same, and the phase angle φ approaches zero, the calculation of the active power P at the end of each phase can be simplified as shown in equation (2):

[0047] (2)

[0048] Where U is the effective value of the voltage at the end of the phase line, and I is the effective value of the current at the end of the phase line. Both can be obtained through voltage and current acquisition (e.g., ...). Figure 4 (As shown).

[0049] In this state, the active power is not sensitive to the measurement error of the phase angle φ, which greatly reduces the systematic calculation error introduced by the inaccuracy of phase measurement.

[0050] In S2 above, the time interval between each time point is determined based on the fluctuation characteristics of the active power at the end of each phase line. If the fluctuation period of the active power at the end of each phase line is long, the time interval is adjusted accordingly to ensure that the data at each time point can track the fluctuation of the active power at the end of each phase line. Based on actual distribution network operation data, the time interval is generally selected within the range of 1 to 3 seconds. The number of time points N is determined according to the data statistical reliability requirements and the total measurement time. To ensure that the loss resistance determined through data fitting has high confidence, a sufficient sample size is required, generally N≥20. Measurements are performed sequentially at each selected time point, and the total measurement time is generally controlled between 1 and 3 minutes.

[0051] In S3 above, the length L of each phase line n The calculation formula is shown in equation (3):

[0052] (3)

[0053] Where R is the loss resistance of the phase line obtained through data fitting, r is the resistance value per unit length of the phase line, and n is the label A, B, or C of each phase line in the line under test.

[0054] In S4 above, the formula for calculating the length L of the line to be tested is shown in equation (4):

[0055] (4)

[0056] Among them, L A L B L C The lengths of each phase of the three-phase lines A, B, and C are measured respectively.

[0057] In this embodiment, high power factor operation is achieved by applying reactive power compensation at the end of each phase of the line under test, ensuring the accuracy of basic measurement data. Random interference is effectively suppressed by using data fitting at multiple time points. Thus, the loss resistance and line length of the distribution line can be accurately measured under normal operating conditions, solving the problem in the prior art that it is impossible to actively perform high-precision length measurement on the operating distribution line.

[0058] The following example illustrates the calculation process of line loss power and line current RMS value in S2 above.

[0059] like Figure 2The diagram shows a distribution network topology including a substation, branch nodes, and transformer substations. This embodiment includes one substation, four transformer substations (substations 1-4), three branch nodes, and multiple straight-line segments connecting the substation, transformer substations, and branch nodes. The straight-line segments without branches are defined as the lines to be tested in this embodiment, and these lines are three-phase lines. For example, the line segment between node 4 and node 3, and the line segment between node 2 and node 1. For the line segment between node 4 and node 3, node 4 is the first measurement node of the line segment, and node 3 is the last measurement node of the line segment.

[0060] Furthermore, in S2 above, the line loss power of each phase line is the difference between the active power at the beginning and the active power at the end of each phase line.

[0061] The formula for calculating the line loss power ΔP of each phase line at each time point is shown in equation (5):

[0062] (5)

[0063] Wherein, P1 is the active power at the beginning of the phase line at that time point, and P2 is the active power at the end of the phase line at that time point.

[0064] In this embodiment, by synchronously measuring the active power at the beginning and end of each phase line at each time point, it can be ensured that the difference between the active power at the beginning and end of each phase line can accurately reflect the line loss power of that phase line.

[0065] Furthermore, in S2 above, the effective value of the line current of each phase line is the root mean square of the effective value of the current at the beginning and the effective value of the current at the end of each phase line.

[0066] From the π-type equivalent circuit of the line, it can be determined that due to the ground admittance of the line, the effective value of the line current in each phase is not equal to the effective value of the current at the beginning or the end. Under high power factor, the approximate calculation formula for the effective value I of the line current in each phase is shown in equation (6):

[0067] (6)

[0068] Wherein, I1 is the effective value of the first current of the phase line at that time point, and I2 is the effective value of the last current of the phase line at that time point.

[0069] In this embodiment, the root mean square of the effective values ​​of the currents at the beginning and end of each phase is used as the effective value of the line current. This approximate formula provides high calculation accuracy under most practical engineering conditions, and is simple to calculate, making it suitable for engineering applications.

[0070] Furthermore, in S3 above, for each phase of the line, the loss resistance of that phase is determined by data fitting using the line loss power and the effective value of the line current at N time points. Specific steps include:

[0071] S31. Calculate the square of the effective value of the line current at each time point for each phase.

[0072] S32. Using the square of the effective value of the line current as the independent variable and the corresponding line loss power as the dependent variable, perform linear regression analysis on the line loss power and the square of the effective value of the line current at the above N time points to obtain the regression equation.

[0073] S33. The slope of the above regression equation is taken as the loss resistance of the phase line.

[0074] In S32 above, the power loss ΔP of each phase line and the effective value I of each phase line current have the relationship shown in equation (7):

[0075] (7)

[0076] Where R is the loss resistance of the phase line, and P0 is the loss other than heat loss. During a single measurement, P0 can be approximated as a constant that is fixed or changes very little.

[0077] Therefore, a linear regression equation can be established between the power loss of each phase line and the square of the effective value of the line current, as shown in equation (8).

[0078] (8)

[0079] Wherein, the independent variable X is the square of the effective value of the current in each phase line, and the dependent variable Y is the power loss of each phase line.

[0080] The slope k and intercept b of the above regression equation are calculated using the least squares method, as shown in equations (9) and (10):

[0081] (9)

[0082] (10)

[0083] in, , The values ​​of the independent and dependent variables at each time point are: , These are the means of the independent variable and the mean of the dependent variable at all time points.

[0084] In this embodiment, linear regression analysis is performed on data from N time points, which can effectively smooth out or suppress random errors caused by measurement noise or small load fluctuations at a single time point, thereby significantly improving the measurement accuracy and reliability of line loss resistance.

[0085] Furthermore, after S3 is completed, a verification step is also included. This involves calculating the coefficient of determination between the line loss power and the square of the effective value of the line current at the N time points. If this coefficient is less than or equal to a preset second threshold, the measurement is deemed invalid. Then, starting from the current moment, N time points are selected again sequentially, and measurements are performed according to S2 and S3. The specific steps include:

[0086] The sum of squares SST of the above linear regression is calculated as shown in equation (11):

[0087] (11)

[0088] in, These are the values ​​of the dependent variable at each time point. This represents the mean of the dependent variable at all time points.

[0089] The sum of squares (SSR) of the linear regression above is calculated as shown in equation (12):

[0090] (12)

[0091] in, These are the regression predictions of the dependent variable at each time point. This represents the mean of the dependent variable at all time points.

[0092] Calculate the coefficient of determination R for the above linear regression. 2 As shown in equation (13):

[0093] (13)

[0094] The calculated coefficient of determination R 2 The linear fit is compared with a preset second threshold to determine whether it is effective. The preset second threshold is set based on statistical principles and is used to determine whether the linear relationship is sufficiently significant. In this embodiment, the threshold can be set to 0.75.

[0095] If the coefficient R is determined 2 If the value is less than or equal to the preset second threshold, the measurement is deemed invalid, indicating that the linear relationship between line loss power and the square of the effective value of line current is weak during the current measurement period, possibly due to sudden load changes or nonlinear interference. Once invalidated, N time points are selected sequentially for measurement starting from the current moment.

[0096] In this embodiment, by calculating the coefficient of determination of the linear fit, the quality of the measured data can be verified, thereby avoiding the misuse of invalid results caused by accidental interference or abnormal operating conditions, and ensuring the reliability of the final data on the resistance and length of each phase line.

[0097] Furthermore, in S3 above, for each phase line, the resistance value per unit length of the phase line is determined based on the current temperature, resistance temperature coefficient, and standard resistance value per unit length of the phase line.

[0098] The formula for calculating the resistance value r per unit length of the line is shown in equation (14):

[0099] (14)

[0100] Where r0 is the standard resistance per unit length of the circuit, which is the DC resistance per unit length of the circuit at the standard reference temperature (20℃), and can be found in the circuit datasheet. α is the temperature coefficient of resistance, which refers to the coefficient by which the resistance of the circuit changes with temperature, and can be determined based on the circuit material or calibrated based on test data. T is the current temperature of the circuit, which can be obtained through temperature acquisition by a temperature sensor (e.g., ...). Figure 4 T0 is the standard reference temperature (20℃).

[0101] In this embodiment, since the line resistance is affected by temperature changes, by considering the influence of the current line temperature on the resistance value per unit length of the line, the systematic error caused by the current line temperature deviating from the standard temperature is eliminated, thus improving the accuracy of the final calculated line length.

[0102] Furthermore, the above measurement method is performed during periods when the line load changes gradually. This period is selected based on the following criterion: the rate of change of active power at the end of the line under test at different time points is less than or equal to 5%. Based on actual operating data of the distribution network, the range of test periods can be determined, generally between 9 PM and 11 PM.

[0103] In this embodiment, measurements are taken during periods of relatively stable line load to ensure the comparability of data measured at each time point, thereby guaranteeing measurement accuracy.

[0104] Secondly, embodiments of this application also provide a power line length measurement system.

[0105] In one embodiment, reference is made to Figure 3 , Figure 3 This is a schematic diagram of a power line length measurement system. Figure 3 As shown, the measurement system includes a first measuring device, a second measuring device, and a reactive power compensation device.

[0106] The first measuring device is positioned at the beginning of the line under test and is used to obtain the active power and effective current values ​​of each phase at the beginning of the line at each time point.

[0107] The second measuring device is located at the end of the line under test and is used to obtain the active power and effective current values ​​at the end of each phase of the line at each time point.

[0108] A reactive power compensation device, configured at the end of the line under test, is used to apply reactive power compensation to the end of each phase of the line under test, so that the power factor at the end of each phase is greater than or equal to a preset first threshold. The line under test is a three-phase line. It is also used to sequentially select N time points at equal intervals, where N > 1; at each time point, the power loss of that phase is determined based on the active power at both ends of that phase, and the effective current value of that phase is determined based on the effective current value at the beginning and / or end of that phase; for each phase, the power loss and the effective current value at the N time points are fitted to determine the power loss resistance of that phase; the length of that phase is determined based on the power loss and the resistance per unit length; and the average length of the three-phase line is calculated as the length of the line under test.

[0109] The first measuring device and the second measuring device can be independent measuring devices that include active power and current RMS measurement functions, or they can be line pole switches (FTUs).

[0110] In this embodiment, by using a first measuring device configured at the beginning of the line and a second measuring device configured at the end of the line, the active power and current effective values ​​of each phase line can be collected synchronously at multiple time points, thereby ensuring the effectiveness of the line loss power and the line current effective value. The reactive power compensation device achieves high power factor operation by applying reactive power compensation at the end of the line under test, ensuring the accuracy of the basic measurement data, and effectively suppresses random interference by using data fitting at multiple time points. Thus, it is possible to accurately measure the line loss resistance and line length under normal operating conditions of the distribution line, solving the problem in the prior art that it is impossible to actively perform high-precision length measurement of the operating distribution line.

[0111] The functions of each module in the aforementioned reactive power compensation device correspond to the steps in the aforementioned power line length measurement method embodiment, and their functions and implementation processes will not be described in detail here.

[0112] In addition, the second measuring device is either an independent measuring device or integrated with the reactive power compensation device.

[0113] like Figure 4 The diagram shows a schematic of a device integrating a second measuring device with a reactive power compensation device. This integrated device includes a power current acquisition module, a data processing module, and a capacitor control module.

[0114] The power and current acquisition module is used to measure the active power and RMS current at the end of the line at various time points.

[0115] The capacitor control module is used to control the capacitor bank to apply reactive power compensation to the end of each phase of the line under test, so that the power factor of the end of each phase is greater than or equal to a preset first threshold.

[0116] The data processing module is used to sequentially select N time points at equal intervals, where N > 1; at each time point, the loss power of the phase line is determined based on the active power at both ends of each phase line, and the effective value of the current of the phase line is determined based on the effective value of the current at the beginning and / or end of each phase line; for each phase line, the loss resistance of the phase line is determined by data fitting through the loss power and effective value of the current at the N time points; the length of the phase line is determined based on the loss resistance and the resistance value per unit length; and the average length of the three phase lines is calculated as the length of the line to be tested.

[0117] It should be noted that the sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0118] The terms "comprising" and "having," and any variations thereof, in the specification, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus. The terms "first," "second," and "third," etc., are used to distinguish different objects, etc., and do not indicate a sequence, nor do they limit "first," "second," and "third" to different types.

[0119] In the description of the embodiments of this application, terms such as "exemplary," "for example," or "for instance" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as "exemplary," "for example," or "for instance" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary," "for example," or "for instance" is intended to present the relevant concepts in a concrete manner.

[0120] In the description of the embodiments of this application, unless otherwise stated, " / " means "or". For example, A / B can mean A or B. The "and / or" in the text is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, in the description of the embodiments of this application, "multiple" means two or more.

[0121] In some processes described in the embodiments of this application, multiple operations or steps are included in a specific order. However, it should be understood that these operations or steps may not be executed in the order they appear in the embodiments of this application, or they may be executed in parallel. The sequence number of the operation is only used to distinguish different operations, and the sequence number itself does not represent any execution order. In addition, these processes may include more or fewer operations, and these operations or steps may be executed sequentially or in parallel, and these operations or steps may be combined.

[0122] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) as described above, and includes several instructions to cause a terminal device to execute the methods described in the various embodiments of this application.

[0123] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for measuring the length of a power line, characterized in that, The method includes: Reactive power compensation is applied to the end of each phase of the line under test so that the power factor at the end of each phase is greater than or equal to a preset first threshold. The line under test is a three-phase line. N time points are selected at equal intervals, where N > 1; at each time point, the power loss of the phase line is determined based on the active power at both ends of each phase line, and the effective value of the current of the phase line is determined based on the effective value of the current at the beginning and / or end of each phase line. For each phase of the line, the loss resistance of that phase is determined by fitting the line loss power and the effective value of the line current at N time points; the length of that phase is determined based on the loss resistance and the resistance value per unit length. The average length of the three-phase line is calculated as the length of the line to be tested.

2. The method for measuring the length of power lines as described in claim 1, characterized in that, The power line includes multiple sections of the line to be tested, each of which is a straight section without branches.

3. The method for measuring the length of power lines as described in claim 1, characterized in that, The line loss power of each phase line is the difference between the active power at the beginning and the active power at the end of each phase line.

4. The method for measuring the length of power lines as described in claim 1, characterized in that, The effective value of the line current of each phase is the root mean square of the effective value of the current at the beginning and the effective value of the current at the end of each phase.

5. The method for measuring the length of power lines as described in claim 1, characterized in that, The method for determining the loss resistance of each phase line by performing data fitting on the line loss power and the effective value of the line current at N time points includes: Calculate the square of the effective value of the line current at each time point for each phase; Using the square of the effective value of the line current as the independent variable and the corresponding line loss power as the dependent variable, a linear regression analysis is performed on the line loss power and the square of the effective value of the line current at the N time points to obtain the regression equation. The slope of the regression equation is taken as the loss resistance of the phase line.

6. The method for measuring the length of power lines as described in claim 5, characterized in that, Calculate the coefficient of determination between the line loss power and the square of the effective value of the line current at the N time points. If the coefficient of determination is less than or equal to a preset second threshold, the measurement is deemed invalid, and N time points are reselected for measurement starting from the current time.

7. The method for measuring the length of power lines as described in claim 1, characterized in that, For each phase line, the resistance value per unit length of the phase line is determined based on the current temperature, temperature coefficient of resistance, and standard resistance value per unit length of the phase line.

8. The method for measuring the length of power lines as described in claim 1, characterized in that, The measurement method is performed during periods when the line load changes gradually.

9. A power line length measurement system, characterized in that, The system includes: The first measuring device is configured at the beginning of the line under test to obtain the active power and effective current values ​​of each phase at the beginning of the line at each time point. The second measuring device is located at the end of the line under test and is used to obtain the active power and effective current values ​​at the end of each phase of the line at each time point. A reactive power compensation device, configured at the end of the line under test, is used to apply reactive power compensation to the end of each phase of the line under test, so that the power factor at the end of each phase is greater than or equal to a preset first threshold. The line under test is a three-phase line. It is also used to sequentially select N time points at equal intervals, where N > 1; at each time point, the power loss of that phase is determined based on the active power at both ends of that phase, and the effective current value of that phase is determined based on the effective current value at the beginning and / or end of that phase; for each phase, the power loss and the effective current value at the N time points are fitted to determine the power loss resistance of that phase; the length of that phase is determined based on the power loss and the resistance per unit length; and the average length of the three-phase line is calculated as the length of the line under test.

10. The power line length measurement system as described in claim 9, characterized in that, The second measuring device is either an independent measuring device or integrated with the reactive power compensation device.

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