A transformer test lead length optimization method based on measured frequency response curve

Abstract

This invention discloses a method for optimizing the length of transformer test leads based on measured frequency response curves, belonging to the field of power equipment condition-based maintenance and high-frequency measurement technology. The method includes: obtaining the physical straight-line distance between the bushing of the transformer under test and the interface of the testing instrument; forming a test loop by connecting the test leads end-to-end through a standard reference load, and obtaining the measured frequency response amplitude curve by frequency sweeping; calculating the spectral fluctuation index and signal attenuation index of the current lead loop; calculating the signal integrity index and determining its applicability through an index mapping model; and deducing the maximum allowable length of the lead based on a target performance threshold, outputting the optimal recommended lead length or triggering an over-limit alarm while meeting the lower limit of the physical distance. This invention can quantify the lead transmission performance and achieve length optimization through a single measurement, effectively avoiding high-frequency attenuation and standing wave distortion caused by the lead, and improving the accuracy and data consistency of frequency response testing.

Description

Technical Field

[0001] This invention belongs to the field of power equipment condition-based maintenance and high-frequency measurement technology, specifically involving a method for optimizing the test lead length of transformers based on measured frequency response curves. Background Technology

[0002] The inspection of power transformer windings is of great significance for the safe operation of the power grid. Frequency response analysis, due to its ability to extremely accurately detect minute displacements and deformations inside the transformer, is widely used in the manufacturing, acceptance, and post-fault diagnosis of transformers.

[0003] In frequency response testing, as the sweep frequency extends into higher frequencies, the test leads are no longer considered ideal conductors but exhibit significant transmission line effects. The longer the lead, the more severe the high-frequency attenuation and standing wave distortion, easily masking the true resonant characteristics of the transformer windings and even leading to misjudgments. However, in complex substation environments, the lead length must meet the physical space constraints of connecting the test instruments to the tall transformer bushings. Currently, field testing often relies on manual experience to select lead lengths, resulting in poor data consistency across different batches. Therefore, accurately quantifying lead attenuation and standing wave distortion based on measured data, and finding the optimal solution between physical connection feasibility and high-frequency signal integrity, is a crucial technical problem that urgently needs to be addressed to improve the standardization of frequency response testing. Summary of the Invention

[0004] The purpose of this invention is to provide a method for optimizing the test lead length of transformers based on measured frequency response curves, so as to solve the problems of lack of quantitative basis for lead length selection and easy distortion of high-frequency data in existing frequency response tests.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for optimizing the test lead length of a transformer based on measured frequency response curves includes the following steps:

[0007] Step 1: Obtain the physical straight-line distance D between the bushing of the transformer under test and the interface of the frequency response test instrument; connect the injection lead and the measurement lead, both of which are of length L, end-to-end through a standard reference load to form a test circuit; use the frequency response tester to perform a broadband frequency sweep and obtain the measured frequency response amplitude curve H(f) characterizing the lead circuit; save it to the host computer.

[0008] Step 2: Calculate the spectral fluctuation index V of the current lead loop using the following formula:

[0009] ;

[0010] In the formula, F represents the high-frequency range of the test; f is the frequency variable; and W(f) is the frequency weighting function. This formula quantifies the impedance mismatch and standing wave ripple distortion caused by lead length.

[0011] Step 3: Calculate the signal attenuation index A of the current lead loop using the following formula:

[0012] ;

[0013] In the formula, ΔF is the bandwidth of the high-frequency test range F; H0(f) is the ideal lossless response curve of the standard reference load. This formula quantifies the average insertion loss of the lead loop in the high-frequency range;

[0014] Step four: Map the spectral fluctuation index V and the signal attenuation index A to the signal integrity index S using the following formula. This index quantifies the signal assurance capability of the current lead condition for high-frequency test results on a percentage basis:

[0015] ;

[0016] In the formula, v and a are the preset fluctuation reference value and attenuation reference value, respectively;

[0017] Step 5: Determine the signal integrity index S: if S≥90, the current lead length is considered excellent; if 70≤S<90, it is considered applicable; if S<70, it is considered transmission distortion.

[0018] Step 6: Combining the target signal integrity index threshold S0, calculate the maximum allowable length L of a single lead under the current test environment using the following formula. max :

[0019] ;

[0020] If D≤L max The recommended length range for the output lead to the host computer is [D, L]. max If D > L max If this occurs, an over-limit alarm will be triggered, and the position of the frequency response test instrument needs to be rearranged.

[0021] Furthermore, in step three, the ideal lossless response curve H0(f) of the standard reference load is obtained by extracting the transmission coefficient amplitude calibrated at the factory of the standard reference load.

[0022] Furthermore, in step two, the frequency weighting function W(f) is calculated by the following formula:

[0023] ;

[0024] In the formula, f0 is the preset characteristic reference frequency, which is taken as the starting frequency of the test high-frequency range F.

[0025] Furthermore, the benchmark parameter calibration method in the evaluation model is as follows: the fluctuation benchmark value v and the attenuation benchmark value a mentioned in step four are obtained by calibrating the maximum tolerable standing wave ripple error limit and the maximum insertion loss limit of the test instrument, respectively.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This invention directly uses field leads to connect standard loads for closed-loop frequency sweeping, innovatively quantifying high-frequency ripple and signal attenuation. It can capture the destructive characteristics of leads on high-frequency transmission signals with extreme precision, and the evaluation results are true and reliable.

[0028] This invention utilizes the physical law that high-frequency errors in coaxial cables accumulate linearly with length. By combining a percentage-based exponential mapping model, the complex cable selection problem is transformed into algebraic calculations. On-site, only a single test and scoring of the existing leads is required to accurately deduce the maximum allowable length that meets high-standard testing requirements, avoiding the tedious process of repeatedly changing cables and making mistakes.

[0029] This invention combines spatial physical constraints with signal quality requirements to construct a feasible domain for leads. It can trigger over-limit alarms under extreme distance conditions, providing valuable on-site guidance and significantly improving the standardization of transformer frequency response testing. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the basic steps of the transformer test lead length optimization method based on measured frequency response curves according to an embodiment of the present invention.

[0031] Figure 2 This is a schematic diagram of the overall layout of the test system according to an embodiment of the present invention.

[0032] The numbers in the diagram are: 1-Transformer under test, 2-Frequency response test instrument, 3-Injection lead, 4-Measurement lead, 5-Standard reference load, 6-Host computer. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific implementation processes. It should be emphasized that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the scope of the present invention's concept and claims.

[0034] Example 1

[0035] This invention provides a method for optimizing the test lead length of a transformer based on measured frequency response curves, such as... Figure 1 and Figure 2 As shown, it includes the following steps:

[0036] Step 1: Obtain the physical straight-line distance D between the bushing of the transformer under test (1) and the interface of the frequency response testing instrument (2). In this embodiment, D = 5m.

[0037] The injection lead 3, with a current length of L=15m, and the measurement lead 4 are connected end-to-end through a broadband passive standard reference load 5 with a characteristic impedance of 50Ω to form a closed-loop test circuit. A broadband frequency sweep is performed using a frequency response tester to obtain the measured frequency response amplitude curve H(f) characterizing the lead circuit, and the curve is saved to the host computer 6.

[0038] Step 2: The host computer 6 extracts the data segment of the measured amplitude curve H(f) within the high-frequency test range F. In this embodiment, the high-frequency range F is set to [1MHz, 10MHz]. The spectral fluctuation index V of the current lead circuit is calculated using the following formula:

[0039] ;

[0040] In the formula, F represents the high-frequency range of the test; f is the frequency variable; and W(f) is the frequency weighting function. This formula quantifies the impedance mismatch and standing wave ripple distortion caused by the lead length.

[0041] The frequency weighting function is as follows:

[0042] ;

[0043] In the formula, f0 is the preset characteristic reference frequency, which is the starting frequency of the test high-frequency range F, i.e., f0 = 1MHz.

[0044] Step 3: Calculate the signal attenuation index A of the current lead loop in the test high-frequency range using the following formula:

[0045] ;

[0046] In the formula, ΔF is the bandwidth of the high-frequency test range F, which is taken as ΔF=9MHz in this embodiment; H0(f) is the ideal lossless response curve of the standard reference load 5, and the transmission coefficient amplitude is extracted from the S-parameter file of the reference load as H0(f). This formula quantifies the average insertion loss of the lead loop in the high-frequency band.

[0047] Step four: Map the spectral fluctuation index V and the signal attenuation index A to the signal integrity index S using the following formula. This index quantifies the signal assurance capability of the current lead condition for high-frequency test results on a percentage basis:

[0048] ;

[0049] In the formula, v and a are the preset fluctuation reference value and attenuation reference value, respectively, which are calibrated by the system in the underlying program according to the hardware performance limit of the selected test instrument. In this embodiment, the maximum allowable ripple is ±0.5dB and the maximum insertion loss is 3dB.

[0050] Step 5: Determine the signal integrity index S: if S≥90, the current lead length is considered excellent; if 70≤S<90, it is considered applicable; if S<70, it is considered transmission distortion.

[0051] Step Six: To further guide the acquisition of optimal test data on-site, the system sets a target signal integrity index threshold S0=90 to meet high-standard test accuracy. The maximum permissible length L of a single lead under the current test environment is calculated using the following formula. max :

[0052] ;

[0053] If D≤L max The recommended length range for the output lead to the host computer 6 is [D, L]. max If D > L max If this occurs, an over-limit alarm will be triggered, and the position of frequency response test instrument 2 needs to be rearranged.

[0054] Furthermore, the calibration method for the benchmark parameters in the evaluation model is as follows: the fluctuation benchmark value v and the attenuation benchmark value a in step four are respectively calibrated by the maximum tolerable standing wave ripple error limit and the maximum insertion loss limit of the test instrument.

[0055] In summary, this invention transforms the complex problem of line selection evaluation into a single pre-test and efficient back-calculation by constructing a feature extraction model and an exponential mapping model based on actual measurements. This method finds a quantitative optimal solution between the feasibility of spatial physical connections and the integrity of high-frequency signals, achieves standardized guidance for the configuration of test lead lengths, and significantly improves the accuracy and data reproducibility of transformer frequency response testing.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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; and these 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.

Claims

1. A method for optimizing the test lead length of a transformer based on measured frequency response curves, characterized in that, Includes the following steps: Step 1: Obtain the physical straight-line distance D between the bushing of the transformer under test (1) and the interface of the frequency response test instrument (2); connect the injection lead (3) and the measurement lead (4) with the current length L to form a test circuit through the standard reference load (5); use the frequency response test instrument to perform broadband frequency sweep, obtain the measured frequency response amplitude curve H(f) characterizing the lead circuit, and save it to the host computer (6). Step 2: Calculate the spectral fluctuation index V of the current lead loop using the following formula: ； In the formula, F is the high-frequency range of the test; f is the frequency variable; W(f) is the frequency weighting function; Step 3: Calculate the signal attenuation index A of the current lead loop using the following formula: ； In the formula, ΔF is the bandwidth of the test high-frequency range F; H0(f) is the ideal lossless response curve of the standard reference load (5); Step 4: Map the spectral fluctuation index V and the signal attenuation index A to the signal integrity index S using the following formula: ； In the formula, v and a are the preset fluctuation reference value and attenuation reference value, respectively; Step 5: Determine the signal integrity index S: if S≥90, the current lead length is considered excellent; if 70≤S<90, it is considered applicable. If S < 70, it is determined to be transmission distortion; Step 6: Combining the target signal integrity index threshold S0, calculate the maximum allowable length L of a single lead under the current test environment using the following formula. max : ； If D≤L max Then the recommended length range for the output lead to the host computer (6) is [D, L]. max If D > L max If this occurs, an over-limit alarm will be triggered.

2. The method according to claim 1, characterized in that, In step three, the ideal lossless response curve H0(f) of the standard reference load (5) is obtained by extracting the transmission coefficient amplitude of the standard reference load (5) as specified by the factory.

3. The method according to claim 1, characterized in that, In step two, the frequency weighting function W(f) is calculated by the following formula: ； In the formula, f0 is the preset characteristic reference frequency.

4. The method according to claim 1, characterized in that, The benchmark parameter calibration method in the evaluation model is as follows: the fluctuation benchmark value v and the attenuation benchmark value a mentioned in step four are obtained by calibrating the maximum tolerable standing wave ripple error limit and the maximum insertion loss limit of the test instrument, respectively.

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