CN105044568B - The fiber ultrasonic detecting system and detection method of self-adaptation type partial discharge of transformer - Google Patents

Abstract

The invention discloses an optical fiber ultrasonic detection system and a detection method for partial discharge of an adaptive transformer. The system includes: the light emitted by a C-band adjustable laser light source enters an optical fiber acoustic emission sensor, and the light is divided into two and enters the first and second photoelectric sensors respectively. The conversion circuit, after processing, obtains the corresponding analog voltage signals. The analog-to-digital conversion circuit processes the analog voltage signals respectively to obtain digital voltage signals. The difference of the digital voltage signal is within the set voltage range; the processed signal is transmitted to the differential amplifier circuit, and the differential amplifier circuit processes the signal and sends the signal to the active filter circuit for output. According to the different splitting ratios and different optical path losses of different sensors, the central wavelength of the laser light source is automatically adjusted, so that the entire measurement system has the best response and dynamic range, and the demodulation circuit maintains a consistent magnification and is conducive to subsequent calibration and Quantify work.

Description

Fiber Optic Ultrasonic Detection System and Method for Adaptive Transformer Partial Discharge

technical field

The invention relates to an optical fiber online acoustic emission (20kHz-200kHz) detection system, in particular to an optical fiber ultrasonic detection system and a detection method for an adaptive transformer partial discharge.

Background technique

In the later period of the power transformer's service life, it is of great significance to realize non-destructive online detection and early warning of faults through its insulation state. Transformer partial discharge is an important means of state detection. Transformer partial discharge ultrasonic signal has a wide spectrum, and most of the energy is concentrated in the 20kHz-250kHz frequency band. Traditional piezoelectric ceramic ultrasonic sensors suffer from severe electromagnetic interference in their measurement results, and are inconvenient to install and measure due to the need for a preamplifier. It is difficult to achieve long-term online measurement in a strong electric field environment. In comparison, fiber optic-based ultrasonic testing technology has more advantages.

The reported acoustic emission sensor based on optical fiber fusion tapered technology has the characteristics of low cost, simple structure, and not affected by temperature drift. However, the coupling period of this kind of sensor is very long, so the static splitting ratio of the sensor is easy to deviate from the preset value. In addition, the optical path loss between different measurement channels cannot be consistent in practical applications, which causes a large difference in the optical power of the two arms of the sensor when it is actually working, so that it is necessary to readjust the static state every time the sensor is replaced. The operating point seriously affects the adaptability, sensitivity and dynamic range of the system.

The reported method of using digital potentiometers can realize automatic gain adjustment, but due to the inconsistency of the magnifications of the two channels in practical applications, the entire measurement system cannot be calibrated.

The published patent CN201310386525.9 "An Acoustic Emission Sensing System Based on a Single-mode Fiber Coupler" uses an ASE broadband light source to achieve fiber-optic ultrasonic measurement, but due to the wide spectral range (40nm) of this type of light source, the measurement The result is that the sensor is averaged over the entire spectral range, and the sensitivity is bound to be reduced compared to a narrow-band source, and its sensitivity at a specific wavelength cannot be quantified, which makes the measurement, calibration and inter-sensor difference of the system difficult. The comparison of performance brings great difficulty.

If a narrow-band light source with a specific wavelength is selected according to the transmission characteristics of the sensor, the ideal measurement effect can also be achieved, and it can be calibrated and compared. However, due to the inconsistent transmission characteristics between sensors, it is not advisable to replace the light source once the sensor is replaced.

Contents of the invention

The purpose of the present invention is to solve the above problems and provide an adaptive optical fiber ultrasonic detection system and detection method for partial discharge of transformers. It provides an optical fiber acoustic emission online detection scheme that uses a narrow-band light source and can realize wavelength scanning and locking. .

In order to achieve the above object, the present invention adopts the following technical solutions:

Adaptive fiber optic ultrasonic detection system for transformer partial discharge, including:

C-band tunable laser light source, the light emitted by the C-band tunable laser light source enters the optical fiber acoustic emission sensor, and the optical fiber acoustic emission sensor divides the light into two, respectively enters the first photoelectric conversion circuit and the second photoelectric conversion circuit,

The first photoelectric conversion circuit and the second photoelectric conversion circuit perform photoelectric conversion processing on the light to obtain corresponding analog voltage signals, and the analog voltage signals are converted into digital voltage signals V1 and V2 through the analog-to-digital conversion circuit, and the digital voltage signals V1 and V2 is sent to the single-chip microcomputer, and the single-chip microcomputer makes a difference between the digital voltage signals V1 and V2, and compares the difference with the set voltage range:

If it exceeds the set voltage range, the single-chip microcomputer sends a command to the C-band tunable laser light source through the serial port, and the C-band tunable laser light source adjusts the central wavelength of the emitted light according to the command, and re-transmits the optical signal. After repeating the above steps, the single-chip microcomputer passes the modulus The conversion circuit samples and compares the photoelectrically converted voltage again, and the cycle continues until the difference between the digital voltage signals V1 and V2 is within the set voltage range;

If the difference is within the set voltage range, the first photoelectric conversion circuit and the second photoelectric conversion circuit will transmit the processed signal to the differential amplifier circuit after the photoelectric conversion process is performed on the light, and the differential amplifier circuit will send the signal to the differential amplifier circuit after processing. To the active filter circuit, and finally the active filter circuit outputs the signal.

The C-band adjustable laser light source, optical fiber acoustic emission sensor, first photoelectric conversion circuit/second photoelectric conversion circuit, analog-to-digital conversion circuit and single-chip microcomputer constitute a closed-loop control, which can be controlled according to different splitting ratios of different optical fiber acoustic emission sensors. Automatically adjust the central wavelength of the C-band tunable laser light source, so that different fiber acoustic emission sensors can maintain a consistent static operating point after access, so that different fiber acoustic emission sensors can maintain the best response and dynamic range after access.

The C-band tunable laser light source (tunalbe laser, UC Company, USA), model GM81022C, has a wavelength adjustment range of 1525-1565 nm.

The optical fiber acoustic emission sensor is an optical fiber acoustic emission sensor manufactured by using optical fiber fusion tapered coupling technology.

The optical fiber acoustic emission sensor is made by a fiber optic tapered machine, and is fixed with a quartz V-shaped groove for the first time after the manufacturing is completed, and then sealed in an aluminum shell.

The coupling period of the optical fiber acoustic emission sensor is 90, the static splitting ratio is 30:70, and the additional loss is 0.5dB.

The adaptive optical fiber ultrasonic detection system for transformer partial discharge is suitable for 20-200khz ultrasonic on-line detection caused by power transformer partial discharge.

An adaptive optical fiber ultrasonic detection method for transformer partial discharge, comprising the following steps:

Step (1): The light at the longest wavelength emitted by the C-band tunable laser light source enters the optical fiber acoustic emission sensor, and the optical fiber acoustic emission sensor divides the light into two, and enters the first photoelectric conversion circuit and the second photoelectric conversion circuit respectively;

Step (2): The first photoelectric conversion circuit and the second photoelectric conversion circuit perform photoelectric conversion processing on the light to obtain corresponding analog voltage signals, and the analog voltage signals are converted into digital voltage signals V1 and V2 through the analog-to-digital conversion circuit, and the digital voltage The signals V1 and V2 are sent to the single-chip microcomputer, and the single-chip microcomputer makes a difference between the digital voltage signals V1 and V2, and compares the difference with the set voltage range;

Step (3): According to the comparison result of step (2), if the difference between the digital voltage signals V1 and V2 is within the set voltage range; after the first photoelectric conversion circuit and the second photoelectric conversion circuit perform photoelectric conversion processing on the light, Both transmit the processed signal to the differential amplifier circuit, and the differential amplifier circuit processes the signal to the active filter circuit, and finally the active filter circuit outputs the signal.

In the step (2), the difference is compared with the set voltage range. If the set voltage range is exceeded, the single-chip microcomputer sends a command to the C-band adjustable laser light source through the serial port, and the C-band adjustable laser light source adjusts the emission according to the command. The central wavelength of the light; the loop continues until the difference between the digital voltage signals V1 and V2 is within the set voltage range.

Beneficial effects of the present invention:

1. Because the demodulation method has automatic wavelength scanning and locking functions, the adjustable light source can be locked on the most sensitive wavelength of the sensor in the C-band through the wavelength scanning method for each sensor, so as to ensure that the measurement system has the most Excellent sensitivity. And the post-stage demodulation circuit has the same gain, so the sensitivity of the sensor at this wavelength can be accurately obtained, and the maximum dynamic range can be maintained, eliminating the influence of the sensor's own characteristics inconsistency and different optical path losses on the measurement system.

2 This demodulation method can obtain the response of each sensor in the scanning spectral range of the tunable light source through the method of wavelength scanning, that is, the optical response characteristics of the optical fiber acoustic emission sensor can be obtained through electronic measurement. The response of the fiber-optic acoustic emission sensor was measured to be consistent. In this way, the response curve of each sensor in the c-band can be obtained, which provides a basis for selecting the sensor.

3 This detection system realizes fiber optic ultrasonic sensing. After replacing sensors with different static splitting ratios, the system also maintains the best sensitivity and dynamic range. It is easy to expand and is suitable for long-term on-line ultrasonic detection of partial discharge of power transformers.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is the output spectrum curve of the optical fiber acoustic emission sensor; wherein, the horizontal axis represents the wavelength, the unit is nm, and the vertical axis represents the light intensity, the unit is dbm;

Figure 3 is the reflection spectrum of the optical fiber acoustic emission sensor with different strains; where the horizontal axis represents the wavelength, in nm, and the vertical axis represents the reflectivity, in dB;

Fig. 4 is the response of the optical fiber acoustic emission sensing system to 100kHz; wherein, the horizontal axis represents time, the unit is S, and the vertical axis represents the output of the detection system, the unit is v.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

According to the characteristics of the tunable laser light source, the wavelength adjustment is always adjusted from large to small. First, the light emitted by the tunable laser light source is controlled to be at the longest wavelength. The light enters the optical fiber acoustic emission sensor, and the light after acoustic wave modulation is divided into two. Respectively enter the two-way photoelectric conversion circuit for processing. The single-chip microcomputer collects the electrical signals converted from the two optical signals and judges them according to the preset judgment conditions. If it is suitable, no adjustment is made. If it is not suitable, the wavelength of the adjustable laser is adjusted by serial port commands to reduce a step size, and then Acquisition and judgment are carried out, and the scanning continues until a suitable central wavelength is found. It can be seen from Figure 2 that within the range of 1525-1565nm, there are at least three wavelength intersection points with the same amplitude in this type of sensor, that is, one of these three wavelengths can be determined. The signal processing circuit performs differential amplification on the two light intensities, and then outputs the final signal through the active filter circuit.

As shown in Figure 1, the light it emits enters the optical fiber acoustic emission sensor and the light is divided into two, and the optical signal modulated by the acoustic wave enters the first photoelectric conversion circuit and the second photoelectric conversion circuit, and the photoelectric conversion circuit converts the received light Converted to voltages V1 and V2, V1 and V2 are respectively converted into digital signals by analog-to-digital converters, and then sent to the single-chip microcomputer, the single-chip microcomputer compares the DC voltage with the preset voltage range, if the value is too small and the difference between the two values is large If the wavelength is too large, it is considered that the wavelength is not suitable, and then the single-chip microcomputer sends a command to the adjustable laser light source through the serial port, and then samples and compares again after increasing a step size, and continues to cycle until V1 and V2 enter the preset range, and the difference between the two channels Also within the preset range. This can ensure good response of the demodulation circuit. After photoelectric conversion, the signal is sent to the differential amplifier circuit for calculation, and then the final signal is obtained through the active filter circuit.

When the fiber optic acoustic emission sensor is affected by external sound waves, the coupling region will generate strain, and the transmission spectrum of the two arms of the fiber optic acoustic emission sensor will also change. According to relevant theories, it can be known that the change of optical power includes the amplitude and frequency information of the acoustic signal.

As shown in Figure 3, the three curves respectively represent the light intensity changes of the two arms of the fiber optic ultrasonic sensor when there is no external strain, 110 microstrain, and 220 microstrain. It can be seen that at 1540nm, 110 and 220 microstrains respectively bring The change of about 0.8dB and 1.3dB can be used to detect the acoustic signal, and the demodulation circuit converts the change of the transmission spectrum into an electrical signal output. As shown in Figure 4, the response of the fiber optic acoustic emission sensing system to 100kHz sine wave excitation.

Although the specific implementation of the present invention has been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, those skilled in the art do not need to pay creative work Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (1)

1. The optical fiber ultrasonic detection method of adaptive type transformer partial discharge is characterized in that, comprises the steps: Step (1): The light at the longest wavelength emitted by the C-band tunable laser light source enters the optical fiber acoustic emission sensor, and the optical fiber acoustic emission sensor divides the light into two, and enters the first photoelectric conversion circuit and the second photoelectric conversion circuit respectively; Step (2): The first photoelectric conversion circuit and the second photoelectric conversion circuit perform photoelectric conversion processing on the light to obtain corresponding analog voltage signals, and the analog voltage signals are converted into digital voltage signals V1 and V2 through the analog-to-digital conversion circuit, and the digital voltage The signals V1 and V2 are sent to the single-chip microcomputer, and the single-chip microcomputer makes a difference between the digital voltage signals V1 and V2, and compares the difference with the set voltage range; Step (3): According to the comparison result of step (2), if the difference between the digital voltage signals V1 and V2 is within the set voltage range; after the first photoelectric conversion circuit and the second photoelectric conversion circuit perform photoelectric conversion processing on the light, The processed signal is transmitted to the differential amplifier circuit, and the differential amplifier circuit processes the signal to the active filter circuit, and finally the active filter circuit outputs the signal; In the step (2), the difference is compared with the set voltage range. If the set voltage range is exceeded, the single-chip microcomputer sends a command to the C-band adjustable laser light source through the serial port, and the C-band adjustable laser light source adjusts the emission according to the command. The central wavelength of the light; it keeps circulating until the difference between the digital voltage signals V1 and V2 is within the set voltage range; The C-band adjustable laser light source, optical fiber acoustic emission sensor, first photoelectric conversion circuit, analog-to-digital conversion circuit and single-chip microcomputer form a closed-loop control, and the C-band adjustable laser light source, optical fiber acoustic emission sensor, and second photoelectric conversion circuit , the analog-to-digital conversion circuit and the single-chip microcomputer also constitute a closed-loop control, which can automatically adjust the central wavelength of the C-band tunable laser source according to the different splitting ratios of different optical fiber acoustic emission sensors, so that different optical fiber acoustic emission sensors can be connected. Best response and dynamic range; The C-band adjustable laser light source is a GM81022C light source with a wavelength adjustment range of 1525-1565nm; The fiber optic acoustic emission sensor is a fiber optic acoustic emission sensor made by using fiber fusion tapered coupling technology; The optical fiber acoustic emission sensor is made by a fiber optic tapered machine, and after the manufacture is completed, it is first fixed with a quartz V-shaped groove, and then sealed in an aluminum shell; The coupling period of the optical fiber acoustic emission sensor is 90, the static splitting ratio is 30:70, and the additional loss is 0.5dB; The adaptive optical fiber ultrasonic detection method for transformer partial discharge is suitable for 20-200khz ultrasonic on-line detection caused by power transformer partial discharge.