Partial discharge ultrasonic detection system and method for automatically compensating system parameter fluctuations

Abstract

The present invention relates to a partial discharge ultrasonic detection system and a method for automatically compensating for system parameter fluctuations. The system comprises a broadband light source, a fiber circulator, an EFPI ultrasonic sensor probe, a beam splitter, a narrowband filter, a photodetector, a data acquisition module, a spectrometer, and a PC processing terminal. The method comprises the following steps: Step A: obtaining measured reflected light spectra; Step B: performing spectral comparison based on cross-correlation theory; Step C: selecting an output channel; Step D: acquiring an electrical signal; and Step E: calculating a compensation signal. Compared to existing technologies, the present invention offers advantages such as higher ultrasonic signal detection frequency and greater ultrasonic signal measurement accuracy.

Description

Technical Field

[0001] The present invention relates to a partial discharge ultrasonic detection technology, in particular to a partial discharge ultrasonic detection system and a method for automatically compensating for system parameter fluctuations. Background Art

[0002] Partial discharge inside power equipment is accompanied by the formation of ultrasonic waves. Therefore, the detection and location of partial discharge can be achieved through ultrasonic detection. The intensity demodulation type EFPI (Extrinsic Fabry-Perot Interferometric) ultrasonic sensor is not affected by environmental noise, has excellent insulation performance, can work stably for a long time, is small in size, and the demodulation response speed meets the requirements of detecting high-frequency ultrasonic signals of hundreds of kHz. Therefore, it is very suitable as a built-in partial discharge detection device. At present, the common intensity demodulation type EFPI ultrasonic sensing system mostly adopts Figure 1 The single-channel structure shown in the figure uses a narrow-band light source with a fixed wavelength as the incident light source. The Fabry-Perot cavity length information is directly demodulated according to the interference light intensity, and then the ultrasonic signal is inferred.

[0003] However, during field use, due to the complex application environment, the initial cavity length of the Fabry-Perot cavity may drift. The above-mentioned system lacks the ability to calibrate the initial cavity length. The drift of the initial cavity length will directly lead to a decrease in detection accuracy. In addition, fluctuations in optical fiber loss and light source power will cause changes in the intensity of light transmitted through the Fabry-Perot cavity, thereby affecting the mapping relationship between the demodulated signal and the ultrasonic signal, and the accuracy of the measurement system will also be reduced. Although some measurement devices have been adjusted to use a broadband light source as input and, based on the phase demodulation method of the optical fiber Fabry-Perot sensor, directly calculate the Fabry-Perot cavity length from the reflected light spectrum and then calibrate the initial cavity length, in actual operation, the spectral resolution, spectral noise and light source type of the spectrometer will affect the accuracy of obtaining the positions of adjacent peaks or troughs, and the calculated cavity length will have a large error.

[0004] Therefore, how to more accurately correct the initial cavity length becomes a technical problem that needs to be solved. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a partial discharge ultrasonic detection system and a method for automatically compensating for system parameter fluctuations.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] According to a first aspect of the present invention, a partial discharge ultrasonic detection system is provided, which is an intensity demodulation EFPI ultrasonic detection system and has the function of automatically compensating for initial cavity length fluctuations and automatically compensating for light source power fluctuations. The partial discharge ultrasonic detection system includes a broadband light source, an optical fiber circulator, an EFPI ultrasonic sensor probe, a spectrometer, a narrowband filter, a photodetector, a data acquisition module, a spectrometer and a PC processing terminal. The optical fiber circulator is respectively connected to the broadband light source, the EFPI ultrasonic sensor probe and the spectrometer, the spectrometer is connected to the narrowband filter, the narrowband filter is respectively connected to the photodetector and the spectrometer, and the data acquisition module and the spectrometer are respectively connected to the PC processing terminal.

[0008] According to a second aspect of the present invention, a method for automatically compensating for system parameter fluctuations of a partial discharge ultrasonic detection system is provided, the method comprising the following steps:

[0009] Step A: Obtaining the measured results of the reflected light spectrum;

[0010] Step B: spectral comparison based on cross-correlation theory;

[0011] Step C: Select output channel;

[0012] Step D: obtaining an electrical signal;

[0013] Step E: Compensation signal calculation.

[0014] As a preferred technical solution, the step A: obtaining the reflected light spectrum is specifically as follows: processing the optical signal transmitted by the EFPI ultrasonic sensor probe through a spectrometer, connecting the unprocessed channel to a spectrometer, and measuring a broadband reflected light spectrum.

[0015] As a preferred technical solution, the optical signal is processed specifically as follows:

[0016] The optical splitter is a 1×N optical splitter having no less than two output channels. Except for one channel, the other channels are respectively connected to narrowband filters with different central wavelengths to process optical signals through different channels.

[0017] As a preferred technical solution, the step B: performing spectral comparison based on cross-correlation theory is specifically as follows:

[0018] The measured reflected light spectrum is compared with the theoretical spectrum corresponding to different cavity lengths for similarity.

[0019] As a preferred technical solution, the similarity comparison is specifically as follows: inputting the measured reflected light spectrum into a PC processing terminal, and performing a comparison based on cross-correlation theory with the theoretical spectra corresponding to different cavity lengths within the linear range through an automatic analysis program.

[0020] As a preferred technical solution, the specific calculation formula for the similarity comparison is as follows:

[0021]

[0022] Where i=0,1,2,3,4……, R i is the measured spectrum and cavity length L i The corresponding cross-correlation coefficient of the theoretical spectrum, I i (λ) is the cavity length L i The corresponding theoretical spectrum.

[0023] As a preferred technical solution, the step C: selecting the output channel is specifically as follows:

[0024] Determine the cavity length L corresponding to the maximum cross-correlation coefficient j , select the cavity length L j The corresponding theoretical spectrum is matched with the central wavelength λ after filtering by a narrowband filter. j Channel j is used as the signal output channel of the ultrasonic detection system.

[0025] As a preferred technical solution, the step D: obtaining electrical signals is specifically as follows: connecting channel 0 and the selected channel j to a photodetector, inputting the measurement signals into a PC processing terminal via a data acquisition module, and obtaining the reflected light intensities of the two channels.

[0026] As a preferred technical solution, the step E: calculating the compensation signal is specifically as follows:

[0027] The ratio of reflected light intensity is obtained through an automatic analysis program:

[0028]

[0029] Where: V is the output voltage after conversion, i j , i0 is the light intensity measured by channel j and channel 0, α j , α0 is the proportional coefficient of channel j and channel 0.

[0030] As a preferred technical solution, the partial discharge ultrasonic detection system is an intensity demodulation EFPI ultrasonic detection system, and has the function of automatically compensating for initial cavity length fluctuations and automatically compensating for light source power fluctuations.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The intensity demodulation EFPI ultrasonic detection system of the present invention can detect and demodulate high-frequency ultrasonic signals of hundreds of kHz (the wavelength demodulation type can only reach tens of kHz), matching the frequency band of ultrasonic signals generated by partial discharge, and has the ability to detect partial discharge ultrasonic signals in power equipment.

[0033] 2. The present invention adopts a wavelength selection method based on cross-correlation to compensate for the initial cavity length. Compared with the conventional phase demodulation method, this method is less affected by the spectral resolution, spectral noise and light source type of the spectrometer, and the error of the obtained initial cavity length is smaller, thereby improving the measurement accuracy of the ultrasonic signal.

[0034] 3. The present invention adopts a light source power fluctuation compensation method based on the light intensity ratio, so that the system output signal is not affected by the light source power and optical fiber transmission loss, and the influence of the proportional coefficient on the fluctuation of the photoelectric device is also greatly reduced, thereby increasing the measurement accuracy of the ultrasonic signal and greatly reducing the probability of false alarm of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of a single-channel structure;

[0036] Figure 2 Schematic diagram of the intensity demodulation EFPI ultrasonic detection system of the present invention;

[0037] Figure 3 Schematic diagrams of examples of initial cavity length compensation results of the present invention, where (a) shows the initial cavity length shifted to 120.14 μm, (b) shows the initial cavity length shifted to 120.18 μm, and (c) shows the initial cavity length shifted to 120.46 μm;

[0038] Figure 4 Schematic diagrams of examples of light source fluctuation compensation results of the present invention: (a) when the light source power fluctuates around 1 mW, (b) when the light source power fluctuates around 2 mW, and (c) when the light source power fluctuates around 3 mW;

[0039] Figure 5 Schematic diagram of an ultrasonic signal measurement example of the present invention, (a) is the time domain waveform, and (b) is the spectrum analysis. DETAILED DESCRIPTION

[0040] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0041] Example 1

[0042] like Figure 2As shown, the intensity-demodulated EFPI ultrasonic detection system of the present invention includes a broadband light source 1, a fiber circulator 2, an EFPI ultrasonic sensor probe 3, a beam splitter 4, a narrowband filter 5, a photodetector 6, a data acquisition module 7, a spectrometer, and a PC processing terminal. These components, including the broadband light source 1, fiber circulator 2, EFPI ultrasonic sensor probe 3, 1×N beam splitter 4, narrowband filter 5, photodetector 6, data acquisition module 7, spectrometer 8, and PC processing terminal 9, form an intensity-demodulated EFPI ultrasonic detection system that automatically compensates for initial cavity length fluctuations and light source power fluctuations.

[0043] The broadband light source 1 has a spectral distribution of Gaussian distribution and a spectral width of not less than 100 nm. The EFPI ultrasonic sensor probe 3 can convert ultrasonic signals into optical signals. The 1×N optical splitter 4 has not less than two output channels, and except for one channel, the other channels are connected to narrowband filters 5 with different central wavelengths.

[0044] The photodetector 6 converts the light intensity signal of the incident light into a voltage signal;

[0045] The automatic compensation of initial cavity length fluctuation can be divided into three steps: actual measurement of reflected light spectrum, spectrum comparison based on cross-correlation theory, and channel selection.

[0046] Step 1: Measure the reflected light spectrum. Connect the channel (channel 0) not connected to the narrowband filter 5 to the spectrometer 8 to measure and obtain the broadband reflected light spectrum distribution I0(λ).

[0047] Step 2: Spectral comparison based on cross-correlation theory. Based on step 1, the measured reflected light spectrum is input into the PC processing terminal 9, and a similarity comparison based on cross-correlation theory is performed with the theoretical spectra corresponding to different cavity lengths within the linear range through an automatic analysis program. The calculation formula is:

[0048]

[0049] Where: R i is the measured spectrum and cavity length L i The corresponding cross-correlation coefficient of the theoretical spectrum, I i (λ) is the cavity length L i The corresponding theoretical spectrum.

[0050] Step 3: Channel selection. Based on step 2, determine the cavity length L corresponding to the maximum cross-correlation coefficient. j , select the cavity length L j The corresponding theoretical spectrum is matched and has a central wavelength λ after filtering by narrowband filter 5 j Channel j is used as the signal output channel of the ultrasonic detection system.

[0051] like Figure 3 As shown in the example, the initial cavity length drifts from 120.32 μm to 120.14 μm, 120.18 μm, and 120.46 μm. The positive and negative peaks of the compensated voltage are symmetrically distributed compared to the average value, and it can be considered that the compensation for the initial cavity length deviation is basically completed.

[0052] The automatic compensation of light source power fluctuation can be divided into two steps: signal acquisition and compensation signal calculation.

[0053] Step 1: Signal Acquisition: After automatically compensating for the initial cavity length fluctuation, channel 0 and the selected channel j are connected to the photodetector 6, and the measurement signals are input to the PC processing terminal 9 via the data acquisition module 7 to obtain the reflected light intensity of the two channels.

[0054] Step 2: Compensation signal calculation. Based on step 1, the ratio of the reflected light intensity is obtained through an automatic analysis program:

[0055]

[0056] Where: V is the output voltage value after conversion, i j , i0 is the light intensity measured by channel j and channel 0, α j , α0 is the proportional coefficient of channel j and channel 0.

[0057] like Figure 4 As shown in the example, the light source power fluctuates by ±500μW at 1mW, 2mW, and 3mW respectively, and the voltage ratio remains almost unchanged. This result shows that the compensation system has a good compensation effect on the light source power fluctuation.

[0058] When the system is 100 cm away from the simulated discharge source, the ultrasonic signal detected by ultrasonic testing is as follows: Figure 5 shown.

[0059] Example 2

[0060] The difference between this embodiment and embodiment 1 is that in this embodiment, the ultrasonic signal detected by ultrasonic detection is 200 cm away from the simulated discharge source. Figure 5 shown.

[0061] Example 3

[0062] The difference between this embodiment and embodiment 2 is that in this embodiment, the ultrasonic signal detected by ultrasonic detection is 300 cm away from the simulated discharge source. Figure 5 shown.

[0063] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for automatically compensating for system parameter fluctuations in a partial discharge ultrasonic detection system, characterized in that: The partial discharge ultrasonic detection system is an intensity demodulation type EFPI ultrasonic detection system, and has the function of automatically compensating for initial cavity length fluctuations and the function of automatically compensating for light source power fluctuations. The partial discharge ultrasonic detection system comprises a broadband light source (1), an optical fiber circulator (2), an EFPI ultrasonic sensor probe (3), an optical splitter (4), a narrowband filter (5), a photoelectric detector (6), a data acquisition module (7), a spectrometer (8) and a PC processing terminal (9). The optical fiber circulator (2) is respectively connected to the broadband light source (1), the EFPI ultrasonic sensor probe (3) and the optical splitter (4). The optical splitter (4) is connected to the narrowband filter (5). The narrowband filter (5) is respectively connected to the photoelectric detector (6) and the spectrometer (8). The data acquisition module (7) and the spectrometer (8) are respectively connected to the PC processing terminal (9). The method comprises the following steps: Step A: Obtaining the measured results of the reflected light spectrum; Step B: spectral comparison based on cross-correlation theory; Step C: Select output channel; Step D: obtaining an electrical signal; Step E: Compensation signal calculation; The step A: obtaining the measured result of the reflected light spectrum is specifically as follows: processing the optical signal transmitted by the EFPI ultrasonic sensor probe (3) through the optical splitter (4), connecting the unprocessed channel to the spectrometer (8), and measuring to obtain a broadband reflected light spectrum; The optical signal is processed specifically as follows: The optical splitter (4) is a 1×N optical splitter having at least two output channels. Except for one channel, the other channels are respectively connected to narrowband filters (5) with different central wavelengths to process optical signals through different channels. The step B: performing spectral comparison based on cross-correlation theory is specifically as follows: Compare the measured reflected light spectrum with the theoretical spectra corresponding to different cavity lengths; The similarity comparison is specifically as follows: inputting the measured reflected light spectrum into a PC processing terminal, and performing a comparison based on cross-correlation theory with the theoretical spectra corresponding to different cavity lengths within the linear range through an automatic analysis program; The specific calculation formula for the similarity comparison is as follows: Where i=0,1,2,3,4……, R i is the measured spectrum and cavity length L i The corresponding cross-correlation coefficient of the theoretical spectrum, I i (λ) is the cavity length L i The corresponding theoretical spectrum.

2. The method according to claim 1, characterized in that The step C: selecting the output channel is specifically as follows: Determine the cavity length L corresponding to the maximum cross-correlation coefficient j , select the cavity length L j The corresponding theoretical spectrum is matched with the central wavelength λ after filtering by a narrowband filter. j Channel j is used as the signal output channel of the ultrasonic detection system.

3. The method according to claim 2, characterized in that The step D: obtaining the electrical signal is specifically as follows: connecting channel 0 and the selected channel j to the photoelectric detector (6), inputting the measurement signal into the PC processing terminal via the data acquisition module, and obtaining the reflected light intensity of the two channels.

4. The method according to claim 1, wherein The step E: calculating the compensation signal is specifically as follows: The ratio of reflected light intensity is obtained through an automatic analysis program: Where: V is the output voltage value after conversion, i j , i0 is the light intensity measured by channel j and channel 0, α j , α0 is the proportional coefficient of channel j and channel 0.

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