A method for evaluating the dielectric loss factor of power equipment under the action of oscillating wave high voltage

Abstract

The present invention discloses a method for evaluating the dielectric loss factor of power equipment under the action of an oscillating wave high voltage, which is applied to the field of high voltage test technology. In addition to evaluating the oscillating wave voltage information in the traditional dielectric loss factor evaluation method, the oscillating wave current is evaluated. Through mathematical deduction, a mathematical expression for the relationship between the dielectric loss factor and the oscillating wave voltage and current waveform parameters is obtained; based on an algorithm combining phase-shifted fast Fourier transform and nonlinear least squares method, the oscillating wave voltage and current sequence is processed to obtain waveform parameter estimates, and then an estimated value of the dielectric loss factor is obtained. The dielectric loss factor evaluation algorithm of the present invention has good anti-noise interference capabilities, and at the same time, the dielectric loss factor estimation accuracy is high.

Description

Technical Field

[0001] The present invention relates to the technical field of high voltage testing, and more particularly to a method for evaluating the dielectric loss factor of electric power equipment under the action of an oscillating wave high voltage. Background Art

[0002] Measuring dielectric loss factor is an effective method for testing the insulation condition of capacitive devices. Using the dielectric loss factor as a characteristic quantity to characterize the overall insulation properties of equipment such as cables, it can identify insulation problems such as aging, moisture, and water treeing, thereby preventing insulation breakdown and power outages caused by degraded insulation. Currently, commonly used methods for measuring dielectric loss factor fall into two main categories: direct and indirect methods. Direct methods, also known as hardware methods, include the zero-crossing comparison method, the bridge method, and the calorie method. Indirect methods, also known as software methods, include the sine fitting method, the correlation function method, and the harmonic analysis method.

[0003] For larger-capacity equipment such as cables and stator windings, oscillating waves, rather than sinusoidal AC excitation, are often used as the excitation power source for withstand voltage and diagnostic tests. Sinusoidal AC excitation either requires high power supply capacity (test transformers) or cannot accurately measure partial discharge due to switching noise (series resonant devices). Oscillating waves, on the other hand, offer advantages such as better consistency with sinusoidal AC, lower power supply requirements, lower size and weight, and the ability to stimulate partial discharge. They are widely used in connection, diagnostic, and preventive testing of capacitive equipment. Years of application and practice have demonstrated that oscillating waves can effectively diagnose insulation faults in capacitive equipment.

[0004] Currently, the dielectric loss factor measurement method applied to oscillating waves is mainly based on the difference in the oscillating wave voltage attenuation coefficient under different dielectric loss factors. The dielectric loss factor is obtained by calculation by mathematically deriving the relationship between dielectric loss and voltage attenuation coefficient, frequency, and resistance representing the loss of the measurement system itself. However, this method has the problem of accurately estimating the resistance representing the loss of the measurement system itself. The lost resistance is related to the amplitude and frequency of the voltage and the capacitance of the test piece. At the same time, the nonlinear loss of the power electronic switch should also be taken into account, and the loss of reactance also varies with different measurement conditions. These problems lead to large measurement errors in the existing methods, and different measurement errors are generated depending on the measurement process. Therefore, how to provide a dielectric loss factor measurement method under oscillating waves that can overcome noise interference in the detection process and improve estimation accuracy is a problem that technical personnel in this field urgently need to solve. Summary of the Invention

[0005] In view of this, the present invention provides a method for evaluating the dielectric loss factor of power equipment under the action of oscillating wave high voltage. Based on the oscillating wave voltage and current sequence, the relationship between the dielectric loss factor and the voltage and current waveform parameters is obtained through mathematical derivation; at the same time, phase-shifted discrete Fourier analysis combined with nonlinear least squares method is used to evaluate the voltage and current waveform parameters, overcoming the noise interference problem and estimation accuracy problem in the detection process, thereby achieving accurate estimation of the dielectric loss factor under oscillating waves.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for evaluating the dielectric loss factor of power equipment under the action of an oscillating wave high voltage comprises the following steps:

[0008] S1, collect oscillation wave voltage sequence X u , current sequence X i ;

[0009] S2, monitoring the oscillating wave voltage sequence X through the sliding window u , current sequence X i The outliers in the vector are replaced by the closest non-outlier elements to obtain the oscillating wave voltage sequence X after outlier processing. u1 , current sequence X i1 ;

[0010] S3, the oscillation wave voltage sequence X after abnormal value processing u1 , current sequence X i1 Converted into a sine wave sequence X u2 、X i2 , and get the estimated value of the attenuation coefficient λ

[0011] S4, for the sine wave sequence X u2 、X i2 Perform phase-shift discrete Fourier analysis to obtain the voltage sequence amplitude U, current sequence amplitude I, angular frequency ω, and initial phase angle φ u 、φ i and the corresponding estimated values

[0012] S5. Estimated value As the initial value, the nonlinear least squares algorithm based on the trust region is used to calculate the oscillation wave sequence X u1 、X i1 Perform parameter evaluation and obtain estimated values

[0013] S6. Based on estimated values Solve for the dielectric loss factor.

[0014] Optionally, the outliers in S2 are sequence points that differ from the median within the sliding window by more than three times the local scaled absolute median difference.

[0015] Optional, S3 specifically:

[0016] S31, oscillating wave voltage sequence X after outlier processing u1 , current sequence X i1 The first ten cycles of data are used as the sequence X of the estimated decay coefficient λ u3 、X i3 ;

[0017] S32, for sequence X u3 、X i3 Perform moving windowing and find the maximum value in the window as the peak value;

[0018] S33, sequence-X u3 、-X i3 Perform moving windowing and find the maximum value in the window as the valley value;

[0019] S34. Calculate an estimated value of the attenuation coefficient λ based on the peak and valley values

[0020] S35. Estimated value based on attenuation coefficient λ Calculate the sine wave sequence X u2 、X i2 .

[0021] Optionally, S4 is:

[0022] S41, for the sine wave sequence X u2 、X i2 Perform shift-add transformation to obtain the sequence X uap 、X iap ;

[0023] S42, sequence X uap 、X iap Perform fast Fourier analysis to obtain an estimated value of the phase

[0024] S43, for the sine wave sequence X u2 、X i2 Perform fast Fourier analysis and transform the sine wave sequence X u2 、X i2 The analysis results and sequence X uap 、X iap Combined with the analysis results, the estimated values ​​of voltage sequence amplitude, current sequence amplitude and frequency are obtained.

[0025] Optionally, S43 specifically includes:

[0026] S431, for the sine wave sequence X u2 、X i2 Perform fast Fourier analysis to obtain the sine wave sequence X u2 、X i2 Discrete spectrum representation of ;

[0027] S432, obtain sequence X uap 、X iap Discrete spectrum representation of ;

[0028] S433, based on the sine wave sequence X u2 and sequence X uap The frequency estimate is calculated by the difference between the main spectral lines of the phase spectrum

[0029] S434, based on the sine wave sequence X u2 and sequence X uap The estimated value of the voltage sequence amplitude is calculated by the discrete spectrum main line spectrum Based on the sine wave sequence X i2 and sequence X iap The estimated value of the current sequence amplitude is calculated by the discrete spectrum main line spectrum

[0030] Optionally, S6 is:

[0031] S61. Based on the equivalent circuit of a capacitive device, write differential equations to obtain expressions for voltage and current.

[0032] S62, solve the attenuation coefficient λ, angular frequency ω, phase difference Parameter expression of ;

[0033] S63. Derive the dielectric loss factor expression based on the voltage and current expressions and the parameter expressions;

[0034] S64, based on estimates Solve for the dielectric loss factor.

[0035] A dielectric loss factor evaluation system under oscillating wave high pressure includes: a waveform measurement module, an abnormal value processing module, an oscillating wave sinusoidalization module, a Fourier analysis module, a parameter evaluation module, and a dielectric loss factor calculation module;

[0036] The waveform measurement module is connected to the abnormal value processing module to collect the oscillation wave voltage sequence X u , current sequence X i ;

[0037] The abnormal value processing module is connected to the oscillation wave sinusoidal module and is used to monitor the oscillation wave voltage sequence X through a sliding window. u , current sequence Xi The outliers in the vector are replaced by the closest non-outlier elements to obtain the oscillating wave voltage sequence X after outlier processing. u1 , current sequence X i1 ;

[0038] The oscillation wave sinusoidalization module is connected with the Fourier analysis module and the parameter evaluation module to convert the oscillation wave voltage sequence X after abnormal value processing u1 , current sequence X i1 Converted into a sine wave sequence X u2 、X i2 , and get the estimated value of the attenuation coefficient λ

[0039] Fourier analysis module, connected to the parameter evaluation module, is used to analyze the sine wave sequence X u2 、X i2 Perform phase-shifted discrete Fourier analysis;

[0040] Parameter evaluation module and dielectric loss factor calculation module are used to analyze the oscillation wave sequence X u1 、X i1 Perform parameter evaluation and obtain estimated values

[0041] Dielectric loss factor calculation module for estimating the Solve for the dielectric loss factor.

[0042] It can be seen from the above technical solution that compared with the prior art, the present invention discloses a method for evaluating the dielectric loss factor of power equipment under the action of oscillating wave high voltage, which has the following beneficial effects: in addition to evaluating the oscillating wave voltage information in the traditional dielectric loss factor evaluation method, the evaluation of the oscillating wave current is added, and the mathematical expression of the relationship between the dielectric loss factor and the oscillating wave voltage and current waveform parameters is obtained through mathematical derivation. Based on the algorithm combining phase-shifted fast Fourier transform and nonlinear least squares method, the oscillating wave voltage and current sequence is processed to obtain a relatively accurate estimate of the waveform parameters, and then the estimated value of the dielectric loss factor is obtained, which has good anti-noise interference ability and high accuracy of dielectric loss factor estimation. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] 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 merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0044] Figure 1This is a flow chart of the dielectric loss factor evaluation method of the present invention;

[0045] Figure 2 is an equivalent circuit diagram of a capacitive device under an oscillation wave of the present invention;

[0046] Figure 3 This is a waveform diagram of the oscillation wave voltage peak detection in an embodiment of the present invention;

[0047] Figure 4 This is a sinusoidal waveform diagram of the oscillating wave voltage and current in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0049] The embodiment of the present invention discloses a method for evaluating the dielectric loss factor of power equipment under the action of oscillating wave high voltage, such as Figure 1 As shown, the following steps are included:

[0050] S1, collect oscillation wave voltage sequence X u , current sequence X i ;

[0051] S2, monitoring the oscillating wave voltage sequence X through the sliding window u , current sequence X i The outliers in the vector are replaced by the closest non-outlier elements to obtain the oscillating wave voltage sequence X after outlier processing. u1 , current sequence X i1 ;

[0052] S3, the oscillation wave voltage sequence X after abnormal value processing u1 , current sequence X i1 Converted into a sine wave sequence X u2 、X i2 , and get the estimated value of the attenuation coefficient λ

[0053] S4, for the sine wave sequence X u2 、X i2 Perform phase-shift discrete Fourier analysis to obtain the voltage sequence amplitude U, current sequence amplitude I, angular frequency ω, and initial phase angle φ u 、φ i and the corresponding estimated values

[0054]

[0055] S5. Estimated value As the initial value, the nonlinear least squares algorithm based on the trust region is used to calculate the oscillation wave sequence X u1 、X i1 Perform parameter evaluation and obtain estimated values

[0056] S6. Based on estimated values Solve for the dielectric loss factor.

[0057] The equivalent circuit of the capacitive device under the oscillating wave in this embodiment is as follows Figure 2 As shown, R1 = 28Ω, L = 1.1H, C = 2.2μF, R2 = 2MΩ data is used to generate an oscillation wave and collect the oscillation wave voltage sequence X u , current sequence X i , the signal-to-noise ratio is 40db, and the theoretical dielectric loss factor true value is tanδ=3.536215e-04;

[0058] Furthermore, the outliers in S2 are sequence points whose difference from the median within the sliding window exceeds three times the local converted absolute median difference.

[0059] Furthermore, S3 is specifically:

[0060] S31, low peak filtering: by controlling the number of cycles of the sequence, using the oscillation wave voltage sequence X after abnormal value processing u1 , current sequence X i1 The first ten cycles of data are used as the sequence X of the estimated decay coefficient λ u3 、X i3 , to avoid low accuracy caused by low signal-to-noise ratio when the peak value is too low;

[0061] S32, Peak Detection: For sequence X u3 、X i3 Perform moving windowing, traverse the entire set of data, and find the maximum value within the window as the peak value to avoid data mismeasurement caused by noise;

[0062] S33, valley detection: for sequence -X u3 、-X i3 Perform moving windowing, traverse the entire set of data, and find the maximum value in the window as the valley value to avoid data mismeasurement caused by noise;

[0063] S34. Calculate an estimated value of the attenuation coefficient λ based on the peak and valley values In this embodiment, the peak and valley values ​​of the voltage are used to calculate the attenuation coefficient λ:

[0064]

[0065] Where U1 and U2 are peak voltages, U3 and U4 are valley voltages, E represents the average value, and t1, t2, t3, and t4 are the times when the voltage reaches U1, U2, U3, and U4, respectively. In this embodiment, the peak voltage detection waveform is as follows: Figure 3 As shown, taking several collected voltage peaks as an example, some peaks with lower amplitudes are ignored, and the estimated value of the attenuation coefficient λ is calculated to be 8.295455.

[0066] S35. Estimated value based on attenuation coefficient λ Calculate the sine wave sequence X u2 、X i2 :The sine wave sequence in this embodiment is as follows Figure 4 shown.

[0067]

[0068] In the formula, t is the independent variable

[0069] Furthermore, S4 is specifically:

[0070] S41, for the sine wave sequence X u2 、X i2 Perform shift-add transformation to obtain the sequence X uap 、X iap ;

[0071] In this embodiment, for a sine wave sequence X with a length of 2N+1, u2 :{x(i),0≤i≤2N-1} is converted to:

[0072]

[0073] Shifting the above formula, we get:

[0074]

[0075] Add the above formula to get the sequence X uap :

[0076] X uap ={Nx(N-1),(N-1)x(N)+x(0),…,(N-1)x(N-2)+x(2N-2)}

[0077] For the sine wave sequence X i2 Perform the above processing to obtain the sequence X iap .

[0078] S42, sequence X uap 、X iap Perform fast Fourier analysis to obtain an estimated value of the phase

[0079] S43, for the sine wave sequence X u2 、X i2 Perform fast Fourier analysis and transform the sine wave sequence X u2 、X i2 The analysis results and sequence X uap 、X iap Combined with the analysis results, the estimated values ​​of voltage sequence amplitude, current sequence amplitude and frequency are obtained.

[0080] In this embodiment, S4 obtains The estimated values ​​are 25004.945640, 35.353929, 642.772235, 1.557612, and 3.140905 respectively. In S5, the nonlinear least squares algorithm based on the trust region is used to calculate the oscillation wave sequence X. u1 、X i1 Perform parameter evaluation and obtain estimated values They are: 8.295454, 642.773690, 1.557602, and 3.140950 respectively.

[0081] Furthermore, S43 is specifically:

[0082] S431, for the sine wave sequence X u2 、X i2 Perform fast Fourier analysis to obtain the sine wave sequence X u2 、X i2 Discrete spectrum representation of ;

[0083] With a sine wave sequence X u2 For example, its discrete spectrum is expressed as:

[0084]

[0085] Among them, Δω is the spectrum accuracy, ω1 is the original signal X u2 The frequency, Φ u1 For X u2 The initial phase angle, F g (kΔω-ω1) is the discrete spectrum of the window function. The window function is a way to truncate the data. Different truncation functions are used to truncate the signal to reduce spectrum energy leakage. The truncation function is called the window function.

[0086] S432, obtain sequence X uap 、X iap Discrete spectrum representation of ;

[0087] With sequence X uap For example, its discrete spectrum is expressed as:

[0088]

[0089] Among them F g (kΔω-ω0) is the discrete spectrum of the window function.

[0090] S433, based on the sine wave sequence X u2 and sequence X uap The frequency estimate is calculated by the difference between the main spectral lines of the phase spectrum

[0091]

[0092] Where k represents the kth spectrum line, τ = (N-1) / 2, and the difference between the main spectrum lines of the phase spectrum is

[0093] S434, based on the sine wave sequence X u2 and sequence X uap The estimated value of the voltage sequence amplitude is calculated by the discrete spectrum main line spectrum Based on the sine wave sequence X i2 and sequence X iap The estimated value of the current sequence amplitude is calculated by the discrete spectrum main line spectrum

[0094] To calculate the estimated value of the voltage series amplitude For example:

[0095]

[0096] In the formula, X(k * ) is the main spectrum line of the discrete amplitude spectrum of X(k), Y(k * ) is the main spectrum line of the discrete amplitude spectrum of Y(k).

[0097] Furthermore, S6 is specifically:

[0098] S61. Based on the equivalent circuit of the capacitive device, write the differential equation to obtain the expression of voltage and current; in this embodiment, based on Figure 2 The equivalent circuit of the capacitive device shown yields the expression:

[0099] u c (t) = U0e -λt cos(ωt+θ);

[0100]

[0101] Where U0 and I0 are the amplitudes of voltage and current respectively, ω is the angular frequency, θ is the initial phase angle of voltage, is the phase difference.

[0102] S62, solve the attenuation coefficient λ, angular frequency ω, phase difference Parameter expression; in this embodiment, the parameter expression is:

[0103]

[0104] S63. Derive a dielectric loss factor expression based on the voltage and current expressions and the parameter expressions. In this embodiment, the dielectric loss factor expression is:

[0105]

[0106] S64, based on estimates Solve for the dielectric loss factor; in this embodiment, the dielectric loss factor is calculated using the following formula:

[0107]

[0108] In this embodiment, the estimated value of the dielectric loss factor is calculated to be 3.536049e-04, and the error from the true value is -0.00469121%.

[0109] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0110] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for evaluating the dielectric loss factor of power equipment under the action of oscillating wave high voltage, characterized in that: The following steps are involved: S1, collect oscillation wave voltage sequence X u , current sequence X i ; S2, monitoring the oscillating wave voltage sequence X through the sliding window u , current sequence X i The outliers in the vector are replaced by the closest non-outlier elements to obtain the oscillating wave voltage sequence X after outlier processing. u1 , current sequence X i1 ; S3, the oscillation wave voltage sequence X after abnormal value processing u1 , current sequence X i1 Converted into a sine wave sequence X u2 、X i2 , and get the estimated value of the attenuation coefficient λ S4, for the sine wave sequence X u2 、X i2 Perform phase-shift discrete Fourier analysis to obtain the voltage sequence amplitude U, current sequence amplitude I, angular frequency ω, and initial phase angle φ u 、φ i and the corresponding estimated values S5. Estimated value As the initial value, the nonlinear least squares algorithm based on the trust region is used to calculate the oscillation wave sequence X u1 、X i1 Perform parameter evaluation and obtain estimated values S6. Based on estimated values Solve for the dielectric loss factor.

2. The method for evaluating the dielectric loss factor of power equipment under the action of an oscillating wave high voltage according to claim 1, characterized in that: Outliers in S2 are sequence points that differ from the median within the sliding window by more than three times the local scaled absolute median difference.

3. The method for evaluating the dielectric loss factor of power equipment under the action of an oscillating wave high voltage according to claim 1, characterized in that: S3 specifically: S31, oscillating wave voltage sequence X after outlier processing u1 , current sequence X i1 The first ten cycles of data are used as the sequence X of the estimated decay coefficient λ u3 、X i3 ; S32, for sequence X u3 、X i3 Perform moving windowing and find the maximum value in the window as the peak value; S33, sequence-X u3 、-X i3 Perform moving windowing and find the maximum value in the window as the valley value; S34. Calculate an estimated value of the attenuation coefficient λ based on the peak and valley values S35. Estimated value based on attenuation coefficient λ Calculate the sine wave sequence X u2 、X i2 .

4. The method for evaluating the dielectric loss factor of power equipment under the action of an oscillating wave high voltage according to claim 1, characterized in that: S4 is specifically: S41, for the sine wave sequence X u2 、X i2 Perform shift-add transformation to obtain the sequence X uap 、X iap ; S42, sequence X uap 、X iap Perform fast Fourier analysis to obtain an estimated value of the phase S43, for the sine wave sequence X u2 、X i2 Perform fast Fourier analysis and transform the sine wave sequence X u2 、X i2 The analysis results and sequence X uap 、X iap Combined with the analysis results, the estimated values ​​of voltage sequence amplitude, current sequence amplitude and frequency are obtained.

5. The method for evaluating the dielectric loss factor of power equipment under the action of an oscillating wave high voltage according to claim 4, characterized in that: S43 is specifically: S431, for the sine wave sequence X u2 、X i2 Perform fast Fourier analysis to obtain the sine wave sequence X u2 、X i2 Discrete spectrum representation of ; S432, obtain sequence X uap 、X iap Discrete spectrum representation of ; S433, based on the sine wave sequence X u2 and sequence X uap The frequency estimate is calculated by the difference between the main spectral lines of the phase spectrum S434, based on the sine wave sequence X u2 and sequence X uap The estimated value of the voltage sequence amplitude is calculated by the discrete spectrum main line spectrum Based on the sine wave sequence X i2 and sequence X iap The estimated value of the current sequence amplitude is calculated by the discrete spectrum main line spectrum 6. The method for evaluating the dielectric loss factor of power equipment under the action of an oscillating wave high voltage according to claim 1, characterized in that: S6 specifically: S61. Based on the equivalent circuit of a capacitive device, write differential equations to obtain expressions for voltage and current. S62, solve the attenuation coefficient λ, angular frequency ω, phase difference Parameter expression of ; S63. Derive the dielectric loss factor expression based on the voltage and current expressions and the parameter expressions; S64, based on estimates Solve for the dielectric loss factor.

Images