Linear cavity optical fiber partial discharge sensing system based on external optical feedback introduction structure

Abstract

The invention belongs to the technical field of electrical measurement. The invention provides a linear cavity optical fiber partial discharge sensing system based on an external optical feedback introduction structure. The linear cavity optical fiber partial discharge sensing system comprises a linear cavity optical fiber laser, an adjustable optical attenuator, a pump laser, a wavelength division multiplexer, an optical isolator, an optical fiber circulator, a 1 * 2 coupler, a 2 * 2 coupler, a balanced photoelectric detector, a filter and an oscilloscope, an external light feedback introduction method is provided based on a semiconductor laser external light feedback theory, and the LCFL obtains the minimum line width by adjusting the introduced light reflectivity, so that the sensitivity of the LCFL is improved, and the problem that the long-distance application sensitivity of the LCFL is reduced due to intrinsic light source characteristics is effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of electrical measurement, and in particular to a linear cavity optical fiber partial discharge sensing system based on an external optical feedback introduction structure. Background Art

[0002] The statements in this section merely provide background art related to the present invention and do not necessarily constitute prior art.

[0003] Partial discharge (PD) is one of the main causes of insulation aging of cables and electrical equipment. Although early PD will not directly cause insulation breakdown of electrical equipment, it will cause rapid insulation degradation and threaten the safe operation of power equipment. Therefore, reliable and effective online PD monitoring methods are of great significance to the operation and maintenance of power equipment and the evaluation of insulation status.

[0004] In recent years, with the development of fiber optic sensing technology and optoelectronic technology, the research on partial discharge detection using fiber optic acoustic wave sensors has increased. The fiber optic partial discharge acoustic wave sensors derived from this mainly include: fiber Bragg grating sensor (FBG), extrinsic fiber Fabry-Perot sensor (EFPI), and fiber interferometer sensor (OFI). The above sensors have their own advantages and can be applied to different monitoring environments, but there are still problems such as low sensitivity, low safety in high electric field environment, and difficulty in spatial separation of the sensing part and the demodulation part.

[0005] Linear cavity fiber laser (LCFL) is a fiber laser with sensing capability that can output a highly coherent light source with an extremely narrow linewidth (<10 kHz). When LCFL is used as a sensing unit, an ultra-high sensitivity close to the thermodynamic limit can be obtained by using a fiber interferometer for signal demodulation. In addition, the LCFL sensing unit and the demodulation system are intrinsically independent, and it is easy to achieve spatial separation of the two when applied to the detection of running power equipment. Compared with the traditional OFI, the detection sensitivity of LCFL is only proportional to the change in the unit length of the resonant cavity and has nothing to do with the absolute length of the resonant cavity. The sensitivity equivalent to that of OFI can be achieved through a sensing length of about 3 cm. However, in actual use, the intrinsic characteristics of the light source of LCFL will cause it to be affected by external light feedback during long-distance detection of partial discharge, resulting in a sharp decline in detection performance. At present, most studies use suppression methods to deal with the influence of external light feedback. This method is simple and practical, but it cannot improve the sensing sensitivity of LCFL, and it still has certain limitations for tiny quantities to be measured. The external light feedback introduction method can adjust the output beam width of LCFL through external light feedback, thereby improving the sensing sensitivity of LCFL, and enhancing the application effect of LCFL. Summary of the invention

[0006] In order to address the deficiencies of the prior art, the present invention provides a linear cavity fiber partial discharge sensing system based on an external light feedback introduction structure, proposes an external light feedback introduction method based on the semiconductor laser external light feedback theory, and enables the LCFL to obtain the minimum line width by adjusting the reflectivity of the introduced light, thereby improving its sensitivity, effectively solving the problem of reduced sensitivity of LCFL in long-distance applications due to the intrinsic light source characteristics.

[0007] In order to achieve the above object, the present invention adopts the following technical solution: A linear cavity fiber partial discharge sensing system with an external optical feedback introduction structure, comprising: a linear cavity fiber laser, an adjustable optical attenuator, a pump laser, a wavelength division multiplexer, an optical isolator, a fiber circulator, Coupler, couplers, balanced photodetectors, filters, and oscilloscopes; The pump laser is connected to the first port of the wavelength division multiplexer, the second port of the wavelength division multiplexer is connected to one end of the linear cavity fiber laser, and the other end of the linear cavity fiber laser is connected to one end of the adjustable optical attenuator; The other port of the adjustable optical attenuator is connected to The first output port of the coupler is connected to the third port of the wavelength division multiplexer The input port of the coupler is connected to the linear cavity fiber laser, the wavelength division multiplexer, The closed loop formed by the coupler and the adjustable optical attenuator is an optical feedback introduction structure; The second output port of the coupler is connected to the input port of the optical isolator, the output port of the optical isolator is connected to the first port of the optical fiber circulator, and the second port of the optical fiber circulator is connected to the A first port of the coupler is connected; The second port of the coupler is connected to a balanced photodetector. The third port of the coupler is connected to the interference arm. The fourth port of the coupler is connected to the reference arm, the interference arm is connected to the first Faraday reflector, and the reference arm is connected to the second Faraday reflector; The third port of the optical fiber circulator is connected to a balanced photoelectric detector, the balanced photoelectric detector is connected to a filter, and the filter is connected to an oscilloscope.

[0008] As a further limitation of the present invention, the crystal rotation angles of the first Faraday reflector and the second Faraday reflector are both 90°.

[0009] As a further limitation of the present invention, the pump laser is a 980nm pump laser, the 980nm pump laser adopts a single-mode pump laser, and the output power of the 980nm pump laser is continuously adjusted within a set range.

[0010] As a further limitation of the present invention, the linear cavity fiber laser is an erbium-ytterbium co-doped linear cavity fiber laser.

[0011] As a further limitation of the present invention, the central wavelength of the linear cavity fiber laser is in the 1550 nm band.

[0012] As a further limitation of the present invention, the Coupler, The splitting ratio of the coupler is 1:1.

[0013] As a further limitation of the present invention, the balanced photodetector is used to combine two optical signals into one electrical signal output, and the detection bandwidth of the balanced photodetector is greater than 100 MHz.

[0014] As a further limitation of the present invention, the filter is a bandpass filter of 60-300 kHz.

[0015] As a further limitation of the present invention, a pump laser, a wavelength division multiplexer, an optical isolator, an optical fiber circulator, Coupler, Couplers, adjustable optical attenuators, balanced photodetectors, and filters are integrated into a vibration-isolated chassis.

[0016] As a further limitation of the present invention, obtaining the grating coupling coefficient of the linear cavity fiber laser , Gate length , Linewidth gain factor , use adjustable optical attenuator to fix external light reflectivity ; According to the external light feedback coefficient calculation formula , is the transmission fiber length, and the linear cavity fiber laser is calculated respectively. and The transmission fiber length value at and , thus determining the transmission fiber length of the optical feedback introduction structure ~ between; The output results of the linear cavity fiber laser before and after the optical feedback introduction structure is connected are compared to verify the successful construction of the optical feedback introduction structure.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Based on the theory of semiconductor laser external light feedback, the present invention proposes an external light feedback introduction strategy. The optical feedback introduction structure is designed with the value of , which effectively solves the problem of long-distance application difficulty caused by the intrinsic light source characteristics of LCFL, and has reference value for optical fiber sensors of the same type with light source properties.

[0018] 2. The external optical feedback introduction structure LCFL optical fiber partial discharge sensing system proposed in the present invention has a simple structure, high safety in high voltage environments, and can be widely adapted to various detection scenarios.

[0019] 3. The introduction of external optical feedback modulates the output line width of LCFL, narrowing the line width of LCFL, greatly improving the detection sensitivity of LCFL, and has important application value in long-distance and small-amount online monitoring.

[0020] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0022] Figure 1 A schematic diagram of the structure of a linear cavity optical fiber partial discharge sensing system with an external optical feedback introduction structure provided by the present invention; Figure 2 A relationship diagram between the external light feedback coefficient and the LCFL output line width provided by the present invention; Figure 3 This is a diagram of the LCFL output result without the introduction of external light feedback provided by the present invention; Figure 4 This is a diagram of LCFL output results when external light feedback is introduced provided by the present invention; Among them, 1. LCFL; 2. WDM; 3. 980nm pump laser; 4. Coupler; 5. Adjustable optical attenuator; 6. 1550nm optical isolator; 7. Fiber circulator; 8. Coupler; 9. First Faraday reflector; 10. Second Faraday reflector; 11. Balanced photodetector; 12. Filter; 13. Oscilloscope. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0024] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0025] In the present invention, a linear cavity optical fiber partial discharge sensing system based on an external optical feedback introduction structure is proposed. Figure 1 As shown, it includes: LCFL1, wavelength division multiplexer 2, 980nm pump laser 3, Coupler 4 (splitting ratio 50:50); adjustable optical attenuator 5 (0-30 dB), 1550nm optical isolator 6, fiber optic circulator 7, A coupler 8 , a first Faraday reflector 9 , a second Faraday reflector 10 , a balanced photodetector 11 , a filter 12 and an oscilloscope 13 .

[0026] In the present invention, the wavelength division multiplexer 2 has three ports, the port marked with 980nm (i.e., the first port of the wavelength division multiplexer 2) is connected to the 980nm pump laser 3, and the third port of the wavelength division multiplexer 2 is connected to the The input port of the coupler 4 is connected, the second port of the wavelength division multiplexer 2 is connected to the first end of the LCFL1, The first output port of the coupler 4 is connected to the tail end of the arrow marked on the 1550nm optical isolator 6. The second output port of the coupler 4 is connected to the first end of the adjustable optical attenuator 5 , and the second end of the adjustable optical attenuator 5 is connected to the second end of the LCFL1 .

[0027] In the present invention, the optical fiber circulator 7 has three ports, the end marked with the arrow tail (i.e., the first port) is connected to the output port of the 1550nm optical isolator 6, the end marked with the arrow (i.e., the third port) is connected to any end of the balanced photodetector 11, and the remaining end (i.e., the second port) is connected to the output port of the 1550nm optical isolator 6. Any end (i.e., the first port) of the coupler 8 is connected, The coupler 8 connects the remaining port (i.e., the second port) on the same side of the optical fiber circulator to the remaining port of the balanced photodetector 11, and the other two ports (i.e., the third port and the fourth port) on the same side are connected to the first Faraday reflector 9 and the second Faraday reflector 10 respectively.

[0028] In the present invention, the electrical signal output end of the balanced photodetector 11 is connected to the filter 12 , and the output end of the filter 12 is output to the oscilloscope 13 , which displays and saves all measurement results.

[0029] When the optical fiber partial discharge sensing system is working, the 980nm pump laser 3 emits pump light through the wavelength division multiplexer 2 and enters the LCFL1. After the doped ions in the LCFL1 absorb the pump light, it emits a very narrow 1550nm band sensing laser. The external measured signal acts on the LCFL1, causing the central wavelength or optical frequency of the sensor laser output by it to change. The signal light (i.e., the first signal light) carries the external measured signal through the wavelength division multiplexer 2, Coupler 4, 1550nm optical isolator 6, fiber optic circulator 7 enter Coupler 8; The second signal light emitted by LCFL1 passes through the adjustable optical attenuator 5. After coupler 4 and wavelength division multiplexer 2, it re-enters LCFL1 to adjust the output laser line width of LCFL1; The coupler 8 divides the signal light into two coherent light beams. One beam passes through the interference arm to reach the first Faraday reflector 9 and then returns along the original path. The other beam passes through the reference arm to reach the second Faraday reflector 10 and then returns along the original path. The two returning light beams are After interference occurs in the coupler 8, the interference light is equally divided into two beams with a phase difference of 180° and then emitted.

[0030] After the two interfering lights enter the balanced photodetector 11, they are converted into electrical signals. Since the two electrical signals have a phase difference of 180°, the balanced photodetector 11 performs a subtraction operation on the two converted electrical signals and outputs an electrical signal to enter the filter 12. The filter 12 performs a 60-300 kHz bandpass filtering on the signal and outputs it as an electrical signal. The electrical signal is used as the detection result of the optical fiber ultrasonic sensor system and is finally collected and displayed by the digital oscilloscope 13.

[0031] In the present invention, the 980nm pump laser 3 is a single-mode pump laser, and the output power of the laser needs to be continuously adjusted within a certain range, so as to adjust the pump laser power according to the output light power of LCFL1.

[0032] In the present invention, the doping ions in LCFL1 are co-doped erbium and ytterbium ions, and the central wavelength is located in the 1550 nm band. The type thereof can use a distributed Bragg reflection fiber laser or a distributed feedback fiber laser.

[0033] In the present invention, The splitting ratio of coupler 8 is 1:1, and the interference arm is 50 m longer than the reference arm.

[0034] In the present invention, the crystal rotation angles of the first Faraday reflector 9 and the second Faraday reflector 10 are both 90°.

[0035] In the present invention, the filter 12 is a 60-300 kHz bandpass filter, which is used to filter out signals outside the partial discharge frequency band.

[0036] In the present invention, the 1550nm optical isolator 6 is a 1550nm band optical isolator with an isolation degree of >28dB. The location of its placement point needs to be determined through strict theoretical calculation. The placement point determination method is based on the semiconductor laser external optical feedback theory. The main idea is to ensure that the output laser of LCFL1 works stably within the external optical feedback coefficient. The value is close to 0 in the front part of region A, thereby eliminating the influence of external light feedback in the guiding fiber.

[0037] In the present invention, Figure 2 As shown in FIG. 1 , the design process of the optical feedback introduction structure includes: Get the grating coupling coefficient of LCFL1 , Gate length , Linewidth gain factor ; The external light reflectivity is fixed at 5 using an adjustable optical attenuator. ; According to the LCFL1 related parameters used in the present invention, the external light feedback coefficient is calculated according to the formula , is the transmission fiber length, and LCFL1 is calculated at and The transmission fiber length value at and , thus determining that the length of the transmission optical fiber introduced into the optical feedback structure is between 15.1 and 32.1 m; The output results of LCFL1 before and after the optical feedback introduction structure design are compared to verify the successful construction of the optical feedback introduction structure. In the present invention, the output results of the linear cavity fiber laser before and after the optical feedback introduction structure design are compared, including: Select a certain length of transmission optical fiber within the range of calculation results and build the optical path in the above manner; The connection relationship between LCFL1, WDM 2, 980nm pump laser 3 and WDM 2 remains unchanged, the connection relationship between balanced photodetector 11 and oscilloscope 13 remains unchanged, the part connected to LCFL1 in the optical feedback introduction structure is disconnected, the output port of 1550nm optical isolator 6 is connected to any port of balanced photodetector 11, all active devices are powered on, and the first output result without external optical feedback introduction is observed on oscilloscope 13. Figure 3 As shown, due to the long-distance application, the output of LCFL1 is extremely noisy, and the external optical feedback introduces a lot of optical feedback noise in the output of LCFL1 that is significantly higher than the background noise.

[0038] The connection relationship among LCFL1, wavelength division multiplexer 2, 980nm pump laser 3, and optical feedback introduction structure remains unchanged, the connection relationship between balanced photodetector 11 and oscilloscope 13 remains unchanged, the output port of 1550nm optical isolator 6 is connected to any port of balanced photodetector 11, all active devices are powered on, and the second output result under the introduction of external optical feedback structure is observed on oscilloscope 13.

[0039] like Figure 4 As shown, after the optical feedback introduction structure is connected, the output of LCFL1 is stable, and there is no noise introduced by external optical feedback. Comparing the first output result with the second output result, when there is no obvious noise in the output result of LCFL1, it indicates that the external optical feedback introduction structure is effective.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A linear cavity optical fiber partial discharge sensing system based on an external optical feedback introduction structure, characterized in that: include: Linear cavity fiber laser, adjustable optical attenuator, pump laser, wavelength division multiplexer, optical isolator, fiber circulator, Coupler, couplers, balanced photodetectors, filters, and oscilloscopes; The pump laser is connected to the first port of the wavelength division multiplexer, the second port of the wavelength division multiplexer is connected to one end of the linear cavity fiber laser, and the other end of the linear cavity fiber laser is connected to one end of the adjustable optical attenuator; The other port of the adjustable optical attenuator is connected to The first output port of the coupler is connected to the third port of the wavelength division multiplexer The input port of the coupler is connected to the linear cavity fiber laser, the wavelength division multiplexer, The closed loop formed by the coupler and the adjustable optical attenuator is an optical feedback introduction structure; The second output port of the coupler is connected to the input port of the optical isolator, the output port of the optical isolator is connected to the first port of the optical fiber circulator, and the second port of the optical fiber circulator is connected to the A first port of the coupler is connected; The second port of the coupler is connected to a balanced photodetector. The third port of the coupler is connected to the interference arm. The fourth port of the coupler is connected to the reference arm, the interference arm is connected to the first Faraday reflector, and the reference arm is connected to the second Faraday reflector; The third port of the optical fiber circulator is connected to a balanced photoelectric detector, the balanced photoelectric detector is connected to a filter, and the filter is connected to an oscilloscope.

2. The linear cavity fiber partial discharge sensing system based on the external light feedback introduction structure according to claim 1, characterized in that: The crystal rotation angles of the first Faraday reflector and the second Faraday reflector are both 90°.

3. The linear cavity fiber partial discharge sensing system based on the external light feedback introduction structure according to claim 1, characterized in that: The pump laser is a 980nm pump laser, the 980nm pump laser adopts a single-mode pump laser, and the output power of the 980nm pump laser is continuously adjusted within a set range.

4. The linear cavity fiber partial discharge sensing system based on the external light feedback introduction structure according to claim 1, characterized in that: The linear cavity fiber laser is an erbium-ytterbium co-doped linear cavity fiber laser.

5. The linear cavity optical fiber partial discharge sensing system based on the external light feedback introduction structure as claimed in claim 4, characterized in that: The central wavelength of the linear cavity fiber laser is located in the 1550 nm band.

6. The linear cavity fiber partial discharge sensing system based on the external light feedback introduction structure according to claim 1, characterized in that: Said The splitting ratio of the coupler is 1:

1. The splitting ratio of the coupler is 1:

1.

7. The linear cavity fiber partial discharge sensing system based on the external light feedback introduction structure according to claim 1, characterized in that: The balanced photoelectric detector is used to combine two optical signals into one electrical signal output, and the detection bandwidth of the balanced photoelectric detector is greater than 100 MHz.

8. The linear cavity optical fiber partial discharge sensing system based on the external optical feedback introduction structure according to claim 1, characterized in that: The filter is a 60-300 kHz bandpass filter.

9. The linear cavity optical fiber partial discharge sensing system based on the external light feedback introduction structure according to claim 1, characterized in that: Pump laser, wavelength division multiplexer, optical isolator, fiber circulator, Coupler, Couplers, adjustable optical attenuators, balanced photodetectors, and filters are integrated into a vibration-isolated chassis.

10. The linear cavity optical fiber partial discharge sensing system based on the external light feedback introduction structure according to claim 1, characterized in that: Obtaining the Grating Coupling Coefficient of Linear Cavity Fiber Lasers , Gate length , Linewidth gain factor , use adjustable optical attenuator to fix external light reflectivity ; According to the external light feedback coefficient calculation formula , is the transmission fiber length, and the linear cavity fiber laser is calculated respectively. and The transmission fiber length value at and , thus determining the transmission fiber length of the optical feedback introduction structure ~ between; The output results of the linear cavity fiber laser before and after the optical feedback introduction structure is connected are compared to verify the successful construction of the optical feedback introduction structure.

Images