Method and device for measuring grounding resistance of power cable based on data curve fitting

Abstract

The invention discloses a power cable grounding resistance measuring method and device based on data curve fitting, and relates to the technical field of high-voltage circuit transmission. According to the method, the resistance value of the shielding layer of the two-phase external shielding grounding can be measured through expansion. According to the method, the measured voltage is the voltage on the capacitor, the change range is large, the voltage can change in the full scale range, the data precision is easy to guarantee, only one measuring loop is needed, and the voltage and the current do not need to be measured at the same time. And meanwhile, the oscillation time is short, the energy attenuation is fast, and a high-power and complex steady-state power supply is not needed.

Description

Technical Field

[0001] The invention discloses a method and a device for measuring the grounding resistance of a power cable based on data curve fitting, and relates to the technical field of high-voltage circuit transmission. Background Art

[0002] Poor grounding of high-voltage power cables can cause discharge of the shield layer, damage the insulation layer, and lead to cable burnout and other faults. In this process, the grounding resistance will change significantly. The power cable cannot be powered off during operation, so the method of detecting the grounding resistance during power outage can only be used during annual maintenance. The traditional method of online measurement of the grounding resistance of power cables is mainly to inject one or several frequencies of voltage or current into the grounding loop of the power cable, and calculate the magnitude of the grounding resistance by detecting the voltage or current value at the grounding end. The injected voltage or current needs to be measured when the circuit reaches a steady state to measure the steady-state voltage and current on the steady-state grounding resistance to calculate the accurate resistance value, so this method requires a relatively large injection power. And because the grounding resistance ranges from tens of milliohms to several ohms, the range of variation is large, and the range of variation of the voltage and current that can be measured on the grounding resistance is also large. When the resistance is small, the measurement accuracy is affected to a certain extent due to the resolution and accuracy limitations of the sampling system. Summary of the invention

[0003] In view of the problems of the prior art, the present invention provides a method and device for measuring the grounding resistance of a power cable based on data curve fitting, and the technical solution adopted is: In a first aspect, a method for measuring grounding resistance of a power cable based on data curve fitting is provided, the method comprising: S1, pre-charge the capacitor and synchronously collect the capacitor voltage in the time domain in the grounding resistance loop through the second-order oscillation; S2, analyzing the device parameters in the second-order circuit by data curve fitting according to the capacitor voltage to obtain the resistance value in the circuit; S3, obtaining a grounding resistance value by subtracting a loop resistance value when the measurement loop is short-circuited from the resistance value.

[0004] In some implementations, in S3, the measurement circuit is short-circuited, specifically including: Two MOSFET devices are used as switches through a single-pole double-throw switch. Rx and Lx are the ground impedances to be measured, the total loop resistance is R, and the total loop inductance is L.

[0005] In some implementations, S1 specifically includes: S11, calculating the residual of each data point and the sum of the variances used in the least squares method according to the initial values ​​of the parameters; S12, calculating the Jacobian matrix of each parameter in the equation at the current moment; S13, calculate the Hessian matrix; S14, iteratively find the next parameter to be found; S15, recalculate the residual, adjust the calculation step size according to the change direction and size of the residual, and then return to S12 for iterative calculation; S16, when the calculation results of two iterations remain approximately unchanged, or the number of iterations reaches a certain value, the solution is terminated and the results are output.

[0006] In some implementations, S12 specifically includes: S121, when the grounding resistance loop When , the voltage equation on the capacitor is: (1) in, , is a parameter to be determined; S122, when the grounding resistance loop , the voltage equation on the root capacitor is: (4).

[0007] In a second aspect, an embodiment of the present invention provides a power cable grounding resistance measurement device based on data curve fitting, the device comprising: The acquisition module is used to pre-charge the capacitor and synchronously acquire the capacitor voltage in the time domain in the grounding resistance loop through the second-order oscillation; An analysis module, used to analyze the device parameters in the second-order circuit by data curve fitting according to the capacitor voltage to obtain the resistance value in the circuit; The processing module is used to obtain the grounding resistance value by subtracting the loop resistance value when the measurement loop is short-circuited according to the resistance value.

[0008] In some implementations, in the processing module, the measurement circuit is short-circuited, specifically including: Two MOSFET devices are used as switches through a single-pole double-throw switch. Rx and Lx are the ground impedances to be measured, the total loop resistance is R, and the total loop inductance is L.

[0009] In some implementations, the acquisition module specifically includes: The initial value unit is used to calculate the residual of each data point and the sum of the variances used in the least squares method according to the initial values ​​of the parameters; Matrix unit 1, used to calculate the Jacobian matrix of each parameter in the equation at the current moment; Matrix unit 2, used to calculate the Hessian matrix; Iteration unit, used for iteratively finding the next parameter to be found; The residual unit is used to recalculate the residual, adjust the calculation step size according to the change direction and size of the residual, and then return to S12 for iterative calculation; The output unit is used to end the solution and output the results when the calculation results of two iterations remain approximately unchanged or the number of iterations reaches a certain value.

[0010] In some implementations, the matrix unit 1 specifically includes: Voltage subunit 1, when the grounding resistance loop When , the voltage equation on the capacitor is: (1) in, , is a parameter to be determined; Voltage subunit 2, when the grounding resistance loop , the voltage equation on the root capacitor is: (4).

[0011] In a third aspect, an embodiment of the present invention provides an electronic device, comprising a memory and a processor, wherein the memory is used to store one or more computer instructions, wherein when the one or more computer instructions are executed by the processor, the method described in the first aspect above is implemented.

[0012] In a fourth aspect, an embodiment of the present invention provides a computer storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, it is used to implement the method described in the first aspect.

[0013] One or more embodiments of the present invention can bring at least the following beneficial effects: The present invention performs a second-order oscillation in the grounding resistance loop after the capacitor is pre-charged, collects a series of capacitor voltages in the time domain in real time and synchronously, solves the parameters of each device in the second-order circuit by data curve fitting, calculates the resistance value in the circuit, and subtracts the loop resistance value when the measurement loop is short-circuited to obtain the grounding resistance value; The method of the present invention can measure the shielding layer resistance value of the two-phase outer shield grounding by extension. The voltage measured by the method of the present invention is the voltage on the capacitor, which has a large variation range and can vary within the full range. The data accuracy is easily guaranteed and only one measurement loop is required, rather than the need to measure the voltage and current at the same time. At the same time, the oscillation time is short, the energy decays quickly, and a large and complex steady-state power supply is not required. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0015] Figure 1 It is a circuit implementation diagram of a method for measuring the grounding resistance of a power cable based on data curve fitting provided by an embodiment of the present invention; Figure 2 The embodiment of the present invention provides Figure 1 Detailed circuit implementation diagram in dashed lines; Figure 3 This is an implementation diagram of an oscillation waveform when the ground resistance is large provided by an embodiment of the present invention; Figure 4 is a schematic diagram of an oscillation waveform when the grounding resistance provided by an embodiment of the present invention is relatively small; Figure 5 It is a schematic diagram of sampling data and fitting curve provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention.

[0017] Embodiment 1: Figure 1 A circuit implementation diagram of a method for measuring the grounding resistance of a power cable based on data curve fitting is shown. Figure 1 As shown, the power cable grounding resistance measurement method based on data curve fitting provided in this embodiment includes: S1, pre-charge the capacitor and synchronously collect the capacitor voltage in the time domain in the grounding resistance loop through the second-order oscillation; S2, analyzing the device parameters in the second-order circuit by data curve fitting according to the capacitor voltage to obtain the resistance value in the circuit; S3, obtaining a grounding resistance value by subtracting a loop resistance value when the measurement loop is short-circuited from the resistance value.

[0018] When the grounding resistance is large, the measured capacitor voltage is an exponential decay curve, and its waveform is as follows Figure 2 When the grounding resistance is small, the measured capacitor voltage is an exponential decay oscillation curve, and its waveform is as shown in Figure 3 shown.

[0019] like Figure 1 As shown, the only controllable device in the entire measurement circuit is capacitor C. After calibration, capacitor C is a fixed value within a certain period of time. U0 is the voltage value at the start time, which can be measured by the measurement circuit and is a known quantity. When the grounding resistance is large, there is ,According to circuit theory, when the capacitor is connected to the measurement circuit at time 0, the voltage equation on the capacitor is: (1) in: (2) (3) The curve is a monotonically decreasing curve, and the capacitor voltage is greater than zero.

[0020] When the grounding resistance is small, there is According to circuit theory, when the capacitor is connected to the measurement circuit at time 0, the voltage equation on the capacitor is: (4) in: (5) (6) (7) (8) At time 0, turn the switch on capacitor C to the ground resistance measurement loop and start the timed sampling. The total amount of sampled data is N (the larger the amount of sampled data, the more accurate the calculation result will be). Analyze the data and calculate the parameters in formula (1) or formula (4). First, analyze the data. If the sampled data are all greater than zero, it means that the ground resistance is large, and use formula (1). Otherwise, it means that the ground resistance is small, and use formula (4).

[0021] Formula (1) and formula (4) are both nonlinear formulas, and it is difficult to calculate their parameters using ordinary data analysis and curve fitting methods. It is also difficult to find an algorithm that can be directly applied in public documents. The inventor applied several optimization algorithms to the present invention respectively. After comparison, the Gauss-Newton optimization algorithm with better effect was finally used to iteratively estimate the parameters in the formula to obtain the parameter values. Since the calculation is performed in an iterative manner, there is no need to solve transcendental equations. Since the capacitance C in this circuit is known, the resistance and inductance values ​​can be calculated based on the parameter values. The calculation process is as follows: Furthermore, S1 specifically includes: S11, calculating the residual of each data point and the sum of the variances used in the least squares method according to the initial values ​​of the parameters; S12, calculating the Jacobian matrix of each parameter in the equation at the current moment; S13, calculate the Hessian matrix; S14, iteratively find the next parameter to be found; S15, recalculate the residual, adjust the calculation step size according to the change direction and size of the residual, and then return to S12 for iterative calculation; S16, when the calculation results of two iterations remain approximately unchanged, or the number of iterations reaches a certain value, the solution is terminated and the results are output.

[0022] The selection of initial values ​​for the Gauss-Newton algorithm is important and determines whether the correct result can be obtained. In the circuit used in the present invention, the capacitance C is a known quantity, and the variation range of the inductance and resistance values ​​in the measurement loop is basically determined. The initial value can be determined according to the component parameters in the circuit (when calculating the initial value, the initial value is determined when the measured ground resistance and ground reactance are zero), and the actual measurement results are all convergent.

[0023] The key to the above steps is to solve the Jacobian matrix J. The calculation of other steps is described in detail in the prior art of Gauss-Newton algorithm. In the present invention, the Jacobian matrix is ​​composed of the gradient of the objective function at each data point. In the sampling result, the measured capacitor voltage value is y.

[0024] When the grounding resistance is large, use formula (1) for calculation. There are two parameters to be determined in formula (1): , , find the unknown coefficients , After that, since the capacitance C is known, the resistance R and inductance L can be calculated according to formulas (2) and (3), completing the order , then formula (1) becomes formula (9): (9) make The residual at : (10) According to the Gauss-Newton method, the least squares method is used to estimate the unknown parameters. ,Right now: (11) Then when When the value satisfies formula (11), it is the optimal value.

[0025] make , , , its Jacobian matrix is ​​a matrix of N rows and 2 columns, and the calculation formula of the elements in the first row and first column is: (12) The calculation of the remaining elements is similar.

[0026] The Jacobian matrix J is: (13) The gradient of is: (14) function The Hessian matrix of is a 2-row 2-column matrix, where The elements are: (15) (16) The iteration formula is: (17) Iterate to or until the specified number of iterations is reached.

[0027] After the calculation is completed, we get , and then use formula (2) and formula (3) to calculate R and L in the measurement loop. After subtracting the inherent resistance and inductance in the loop, the ground resistance and ground inductance values ​​can be obtained.

[0028] When the grounding resistance is small, use formula (4) to calculate: Known, let , , , , transform formula (4) into formula (18): (18) Let the residual at t=t: (19) According to the Gauss-Newton method, the least squares method is used to estimate the unknown parameters, that is: (20) Then when , when the value satisfies formula (20), it is the optimal value.

[0029] There are four unknown parameters in formula (20): ,make 7, , , its Jacobian matrix is ​​a matrix with N columns and 4 rows, and the calculation formula for the elements in the first row and first column is: (twenty one) The calculation of the remaining elements is similar.

[0030] The Jacobian matrix J is: (twenty two) The gradient of is: (twenty three) function The Hessian matrix of is a matrix with 4 rows and 4 columns. The elements are: (twenty four) (25) The iteration formula is: (26) Iterate to or until the specified number of iterations is reached.

[0031] In actual testing, no The matrix is ​​ill-conditioned and cannot be inverted, but in order to ensure The matrix is ​​reversible, and the Levenberg-Marquardt method can be applied in formula (26) to correct the calculation process, but it has no effect on the result. Is it a positive definite matrix? If it is not positive definite, then the eigenvalue λmin<0, take a sufficiently small positive number e, and take: (27) The correction method of formula (27) is not currently applied in the present invention F.

[0032] After the calculation is completed, we get , and then use formula (5-8) to calculate R and L in the measurement loop. After subtracting the inherent resistance and inductance in the loop, the grounding resistance and grounding inductance values ​​can be obtained.

[0033] The above method is used to obtain the oscillation waveform in the circuit using a simulation loop. The initial capacitor voltage is 150V, the capacitance is 500 microfarads, the sampling frequency is 100KHz, and curve fitting is performed based on the sampling data to obtain the waveform of the data and the curve as shown in Figure 4. The resistance in the simulation circuit is 0.1 ohm. Based on the calculated parameters, the resistance R=0.1022 ohm is calculated using formula (5-8), and the inductance L is 50 microhenry. The measured resistance error is 2.2%.

[0034] At the same time, through simulation data and actual measurement experiments, it is found that correct results can still be obtained in situations with large interference, but the number of iterations increases significantly and the amount of calculation increases; when single-precision floating-point numbers are used for calculation, the convergence time is long and the accuracy is not as good as using double-precision floating-point numbers.

[0035] Embodiment 2: In a second aspect, an embodiment of the present invention provides a power cable grounding resistance measurement device based on data curve fitting, the device comprising: The acquisition module is used to pre-charge the capacitor and synchronously acquire the capacitor voltage in the time domain in the grounding resistance loop through the second-order oscillation; An analysis module is used to analyze the device parameters in the second sister circuit by data curve fitting according to the capacitor voltage to obtain the resistance value in the circuit; The processing module is used to obtain the grounding resistance value by subtracting the loop resistance value when the measurement loop is short-circuited according to the resistance value.

[0036] Further, in the processing module, the measurement circuit is short-circuited, specifically including: Two MOSFET devices are used as switches through a single-pole double-throw switch. Rx and Lx are the ground impedances to be measured, the total loop resistance is R, and the total loop inductance is L.

[0037] Furthermore, the acquisition module specifically includes: The initial value unit is used to calculate the residual of each data point and the sum of the variances used in the least squares method according to the initial values ​​of the parameters; Matrix unit 1, used to calculate the Jacobian matrix of each parameter in the equation at the current moment; Matrix unit 2, used to calculate the Hessian matrix; Iteration unit, used for iteratively finding the next parameter to be found; The residual unit is used to recalculate the residual, adjust the calculation step size according to the change direction and size of the residual, and then return to S12 for iterative calculation; The output unit is used to end the solution and output the results when the calculation results of two iterations remain approximately unchanged or the number of iterations reaches a certain value.

[0038] Furthermore, in the matrix unit 1, the calculation equation is as follows: (1) in, , To be determined parameter.

[0039] Embodiment three: This embodiment further provides an electronic device, including a memory and a processor, wherein the memory is used to store one or more computer instructions, wherein the one or more computer instructions implement the method of embodiment 1 when executed by the processor; In practical applications, the processor can be an application specific integrated circuit (ASIC), a digital signal processor (DSP), a digital signal processing device (DSPD), a programmable logic device (PLD), a field programmable gate array (FPGA), a controller, a microcontroller unit (MCU), a microprocessor or other electronic components to execute the methods in the above embodiments.

[0040] The method implemented in this embodiment is as shown in the content of the first embodiment. Embodiment 4: This embodiment further provides a computer storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by one or more processors, the method of the first embodiment is implemented; Among them, the computer-readable storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, magnetic disk or optical disk.

[0041] The method implemented in this embodiment is as shown in the content of the first embodiment. In the several embodiments provided in the embodiments of the present invention, it should be understood that the disclosed system and method can also be implemented in other ways. The system and method embodiments described above are merely illustrative.

[0042] It should be noted that, in this article, the terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. The terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0043] Although the embodiments disclosed in the present invention are as above, the above contents are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A method for measuring the grounding resistance of a power cable based on data curve fitting, characterized in that: The method comprises: S1, pre-charge the capacitor and synchronously collect the capacitor voltage in the time domain in the grounding resistance loop through the second-order oscillation; S2, analyzing the device parameters in the second-order circuit by data curve fitting according to the capacitor voltage to obtain the resistance value in the circuit; S3, obtaining a grounding resistance value by subtracting a loop resistance value when the measurement loop is short-circuited from the resistance value.

2. The method according to claim 1, characterized in that In S3, the measurement circuit is short-circuited, specifically including: Two MOSFET devices are used as switches through a single-pole double-throw switch. Rx and Lx are the ground impedances to be measured, the total loop resistance is R, and the total loop inductance is L.

3. The method according to claim 1, characterized in that S1 specifically includes: S11, calculating the residual of each data point and the sum of the variances used in the least squares method according to the initial values ​​of the parameters; S12, calculating the Jacobian matrix of each parameter in the equation at the current moment; S13, calculate the Hessian matrix; S14, iteratively find the next parameter to be found; S15, recalculate the residual, adjust the calculation step size according to the change direction and size of the residual, and then return to S12 for iterative calculation; S16, when the calculation results of two iterations remain approximately unchanged, or the number of iterations reaches a certain value, the solution is terminated and the results are output.

4. The method according to claim 3, characterized in that S12 specifically includes: S121, when the grounding resistance loop When , the voltage equation on the capacitor is: （1） in, , is a parameter to be determined; S122, when the grounding resistance loop , the voltage equation on the root capacitor is: (4)。 5. A power cable grounding resistance measuring device based on data curve fitting, characterized in that: The device comprises: The acquisition module is used to pre-charge the capacitor and synchronously acquire the capacitor voltage in the time domain in the grounding resistance loop through the second-order oscillation; An analysis module, used to analyze the device parameters in the second-order circuit by data curve fitting according to the capacitor voltage to obtain the resistance value in the circuit; The processing module is used to obtain the grounding resistance value by subtracting the loop resistance value when the measurement loop is short-circuited according to the resistance value.

6. The device according to claim 5, characterized in that In the processing module, the measurement circuit is short-circuited, specifically including: Two MOSFET devices are used as switches through a single-pole double-throw switch. Rx and Lx are the ground impedances to be measured, the total loop resistance is R, and the total loop inductance is L.

7. The device according to claim 5, characterized in that The acquisition module specifically includes: The initial value unit is used to calculate the residual of each data point and the sum of the variances used in the least squares method according to the initial values ​​of the parameters; Matrix unit 1, used to calculate the Jacobian matrix of each parameter in the equation at the current moment; Matrix unit 2, used to calculate the Hessian matrix; Iteration unit, used for iteratively finding the next parameter to be found; The residual unit is used to recalculate the residual, adjust the calculation step size according to the change direction and size of the residual, and then return to S12 for iterative calculation; The output unit is used to end the solution and output the results when the calculation results of two iterations remain approximately unchanged or the number of iterations reaches a certain value.

8. The device according to claim 7, characterized in that The matrix unit 1 specifically includes: Voltage subunit 1, when the grounding resistance loop When , the voltage equation on the capacitor is: （1） in, , is a parameter to be determined; Voltage subunit 2, when the grounding resistance loop , the voltage equation on the root capacitor is: (4)。 9. An electronic device, characterized in that: The invention comprises a memory and a processor, wherein the memory is used to store one or more computer instructions, wherein the one or more computer instructions, when executed by the processor, implement the method as described in any one of claims 1 to 4.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, it is used to implement the method as described in any one of claims 1 to 4 above.

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