CN116223389A - High-reliability optical fiber detection system for dissolving acetylene in transformer oil - Google Patents

Abstract

The invention discloses a high-reliability optical fiber detection system for dissolved acetylene in transformer oil, which is a high-reliability in-situ online monitoring system for dissolved acetylene in transformer oil based on double Mach-Zehnder heterodyne interference topology and an oil core photonic crystal optical fiber. Comprising the following steps: the device comprises a light source module, an oil dissolved gas sensing module and a data demodulation module. The system is based on the photothermal spectrum principle, adopts an oil core photonic crystal fiber as a sensing unit, and a plurality of micron-sized micropores are drilled on the side surface of the fiber along the axial direction, so that transformer oil is allowed to enter the fiber core, and the system can be directly arranged in a transformer oil tank to realize in-situ detection of dissolved acetylene. The system utilizes the improved Mach-Zehnder heterodyne interference structure to form a double Mach-Zehnder heterodyne interference topology, and can directly eliminate noise interference such as external ultrasound, vibration and the like by combining a data demodulation module, so that the dissolved acetylene sensing in the transformer oil with high reliability is realized, the running state of the transformer is further evaluated, and early fault early warning is realized.

Description

A high-reliability optical fiber detection system for dissolved acetylene in transformer oil

technical field

The invention belongs to the technical field of optical sensing systems, and in particular relates to a high-reliability optical fiber detection system for dissolving acetylene in transformer oil.

Background technique

The power transformer is the core equipment in the operation of the power grid. Accidents caused by transformer failures occur from time to time. Therefore, monitoring the operation status of power transformers is the key to ensuring the safe operation of the power grid. At present, oil-immersed transformers are commonly used in high-voltage and large-capacity power transformers at home and abroad, and the analysis of dissolved gases in oil is the primary method for detecting faults in oil-immersed transformers. Among the fault characteristic gases, acetylene is one of the important characteristic gases reflecting low-energy spark discharge and high-energy arc discharge. Therefore, on-line monitoring of dissolved acetylene in transformer oil is an important means to realize early fault warning and has important engineering significance.

The traditional method for analyzing dissolved gas in transformer oil mainly uses gas chromatography, which is an off-line detection method. This process requires oil to be taken from the oil inlet of the transformer, and then vacuum degassing method or headspace degassing method is used to separate oil and gas. , and collect gas samples, and finally use a gas chromatograph for detection. The above-mentioned process is complicated to operate, and the process from the generation of the fault characteristic gas to the dissolution into the oil and diffusion to the oil inlet when the transformer fault occurs takes a long time, usually tens of hours, and the gas sample is greatly affected during the sampling and degassing process. Large, there may be large errors in the measurement results.

In recent years, gas online monitoring technology based on optical fiber sensing technology has developed rapidly, mainly including: photoacoustic spectroscopy, direct absorption spectroscopy, Raman spectroscopy and photothermal spectroscopy. However, when the above-mentioned optical technology is used to directly detect the dissolved acetylene in the transformer oil, there are the following problems.

(1) The above-mentioned optical fiber detection technologies are all detected in a gas phase environment, and the detection of dissolved acetylene in oil still needs to involve the oil-gas separation process, so there is still a problem of time-consuming.

(2) Since there is a lot of noise interference in the operating environment of the transformer, especially noise such as ultrasound and vibration, which cannot be avoided or completely filtered out by means of filtering, it is very easy to cause large errors in the detection results when using the above-mentioned detection technology for gas monitoring .

(3) According to the requirements of SD 187-86 "Guidelines for Analysis and Judgment of Dissolved Gas in Transformer Oil", the attention value of transformer fault characteristic gas is usually several ppm, so the detection limit needs to reach the level of one part per million. Very demanding.

In view of the above problems, it is necessary to propose a high-reliability in-situ online monitoring system for dissolved acetylene in oil that can adapt to the transformer operating environment and overcome noise interference, so as to realize early warning of transformer failures.

Contents of the invention

The object of the present invention is to propose a high-reliability optical fiber detection system for acetylene dissolved in transformer oil, which is characterized in that it consists of a light source module, a dissolved gas sensing module in oil, and a data demodulation module. The light source module is divided into a pump light part and a probe light part. The pump light part includes: a light source controller, a pump laser, an erbium-doped fiber amplifier, and an optical circulator. The probe light part includes a probe laser and an optical isolator. The sensor module for dissolved gas in oil uses an oil-core photonic crystal fiber with several micron-sized holes drilled along the axial direction as the sensing unit, which is directly built into the transformer oil tank, and an improved Mach-Zendr sensor module is built based on photothermal spectroscopy technology. The heterodyne interference structure forms a dual Mach-Zehnder heterodyne interference topology, which can directly eliminate external noise interference and realize highly reliable sensing of acetylene dissolved in transformer oil. The data demodulation module is composed of balanced photodetector 1, balanced photodetector 2, phase detector, data acquisition card and computer, which can realize fast real-time demodulation of dissolved acetylene concentration signal.

In the light source module, the pump light laser is controlled by the light source controller to emit pump light whose light intensity is continuously sinusoidally modulated, and the wavelength is located at the strongest absorption of acetylene, and the pump light is amplified by the erbium-doped fiber amplifier and then passed through the optical circulator Enter the oil-core photonic crystal fiber, which is used to interact with the dissolved acetylene inside the fiber core to stimulate the photothermal effect; the probe light emitted by the probe light laser is located at the weakest absorption point of acetylene, and enters the double Mach-Zehnder heterodyne interference structure through the optical isolator .

Preferably, the pump laser is controlled by the light source controller to emit continuous sinusoidal modulated light with a wavelength of 1530.37nm and an average power of not less than 5mW, and the light intensity modulation frequency is not lower than 20kHz, and the wavelength is located at the P(9) absorption line of acetylene, namely Where the absorption of acetylene is strong; the detection laser emits continuous light with a wavelength of 1550nm and a power of not less than 20mW, and this wavelength is located at the place where the absorption of acetylene is weak.

Preferably, the amplified optical wavelength range of the erbium-doped fiber amplifier is 1500nm to 1670nm, the saturated output power is not lower than 20dBm, and the maximum gain multiple is not lower than 30dB, and the amplifier works in automatic gain control mode to ensure that the amplified input to The pump light power in the oil-core photonic crystal fiber is not lower than 90mW.

In the sensor module for dissolved gas in oil, the oil-core photonic crystal fiber is used as the sensing unit, and the oil-core photonic crystal fiber is drilled with a number of micron-scale micro-holes as deep as the central core along the axial direction. The fiber can be directly put into the transformer oil for In-situ detection, the side microholes allow the transformer oil carrying dissolved acetylene molecules to directly enter the central core area of the oil-core photonic crystal fiber and a small number of air holes in the cladding. The refractive index of the transformer oil in the central core area is higher than that of the cladding. Constituting the optical fiber total internal reflection mechanism, no less than 95% of the laser light can be effectively confined and propagated in the central core region of the oil-core photonic crystal fiber, realizing low-loss centralized transmission.

Preferably, the oil-core photonic crystal fiber is made of a hollow-core photonic crystal fiber with a model number of HC-1550-02, the length of which is not less than 0.8m, the optical wavelength transmission range is 1490nm-1680nm, and the optical transmission loss does not exceed 30dB /km.

Preferably, the oil-core photonic crystal fiber uses femtosecond laser technology to drill a number of micro-holes as deep as the central core area every 10 cm along the side axis, the diameter of the micro-holes is not less than 3 μm and not more than 4 μm, and the loss of a single hole is not less than 4 μm. More than 0.2dB, to ensure oil exchange inside and outside the core of the oil-core photonic crystal fiber and low-loss transmission of light inside the core.

Preferably, the two ends of the oil-core photonic crystal fiber are fusion-connected to the ordinary single-mode fiber with low loss, and the single fusion loss does not exceed 2dB, and the cladding air holes at both ends are fused and closed during fusion to prevent the transformer oil from fused from the two ends. Access to cladding air holes.

The dissolved gas in oil sensing module is mainly based on the principle of photothermal spectroscopy, through the improved heterodyne interference structure, a dual Mach-Zehnder heterodyne interference topology is formed, and the data demodulation module can effectively avoid the interference of the transformer operating environment noise .

The dual Mach-Zehnder heterodyne interference topology includes two optical paths: sensing heterodyne interference and reference heterodyne interference. The optical paths of the two are basically the same, and the same oil-core photonic crystal fiber is used as the sensing unit, both of which are directly placed in the fuel tank The same area inside, the difference is that the pump light enters the oil-core photonic crystal fiber 1 through the optical circulator and interacts with the dissolved acetylene inside the fiber core to excite the photothermal effect to generate a phase modulation signal, while the oil-core photonic crystal fiber 2 has no pump When light enters, the photothermal effect is not excited. The probe light is divided into two paths through the 1×2 coupler 1, and one path is used as the sensing light, which is divided into two paths by the 1×2 coupler 2 and enters two oil-core photonic crystal fibers; the other path is used as the reference light, and is modulated by acousto-optic After the frequency shift, the 1×2 coupler 3 is divided into two paths, which interfere with the two beams of sensing light at the 2×2 coupler 1 and the 2×2 coupler 2 respectively. Finally, a sensing interference light signal with dissolved acetylene concentration information in oil and oil environmental noise information and a reference light interference signal with only transformer oil environmental noise noise information are formed, which are respectively detected by the balanced photodetector 1 and the balanced photodetector The device 2 collects and converts electrical signals.

Preferably, the frequency shift of the acousto-optic modulator is not lower than 100MHz, and modulates the phase modulation signal to a high frequency to avoid system pink noise interference.

Preferably, the splitting ratios of the 1×2 couplers 1, 2, 3 and the 2×2 couplers 1, 2 are all 50:50.

In the data demodulation module, the two interference signals are respectively converted into electrical signals by their respective balanced photodetectors and then directly input to the phase detector as two input signals, and the phase detector compares the zero-crossing points of the two signals to obtain a phase difference, The output signal is the phase difference time-domain signal of the two interference signals, which only contains the concentration information of dissolved acetylene in the oil, which is further collected by the data acquisition card and processed by the computer Fourier transform to directly obtain the signal reflecting the concentration information of acetylene.

Preferably, the bandwidth of the phase detector is not lower than 500MHz, the output voltage ranges from 0V to 1.8V, and the output signal can effectively represent the phase difference change of the two input signals.

Compared with the prior art, the present invention has beneficial effects.

(1) Real-time in-situ detection of dissolved acetylene in transformer oil can be realized. The invention adopts the oil-core photonic crystal optical fiber with micron-scale microholes drilled in the axial direction as the sensing unit, which can be directly placed inside the transformer oil tank without involving any form of oil-gas separation process; the transformer oil carrying dissolved acetylene can be directly Entering the inside of the optical fiber core, it overcomes the time-consuming problem of oil and gas separation process in the traditional detection of dissolved acetylene, thus realizing in-situ real-time detection.

(2) Strong anti-interference ability. The present invention introduces a dual Mach-Zehnder heterodyne interference topology into the dissolved gas sensing module in oil, the frequency of the two interference signals is the same, and the phase difference is only the photothermal phase modulation signal caused by dissolved acetylene, which can directly avoid partial discharge ultrasonic and vibration and other sudden interference signal noise, greatly improving the reliability of the system detection results.

(3) The lower limit of detection is low. The invention combines the photothermal spectrum technology with the heterodyne interference structure, which has a lower detection limit for small signal detection, and at the same time modulates the phase signal to high frequency through the acousto-optic modulator, effectively reducing the 1/ f noise interference of the detection system , so the direct detection of dissolved acetylene in transformer oil at the ppm level can be achieved.

Description of drawings

In order to make the effect and technical implementation of the present invention easier to understand, the following will be described in detail in conjunction with the accompanying drawings.

Figure 1 shows the topology of a high-reliability optical fiber detection system for dissolved acetylene in transformer oil.

Figure 2 is a schematic diagram of the arrangement of sensing elements.

Fig. 3 is a schematic diagram of the structure of an oil-core photonic crystal fiber.

Detailed ways

The invention provides a high-reliability optical fiber detection system for dissolving acetylene in transformer oil, which will be described below with reference to the accompanying drawings.

Referring to Fig. 1, an embodiment of the present invention provides a high-reliability optical fiber detection system for acetylene dissolved in transformer oil, including a detection laser, an optical isolator, a 1×2 coupler 1, a 1×2 coupler 2, an oil Core photonic crystal fiber 1, oil core photonic crystal fiber 2, optical circulator, acousto-optic modulator, 1×2 coupler 3, 2×2 coupler 1, 2×2 coupler 2, light source controller, pump laser , Erbium-doped fiber amplifier, balanced photodetector 1, balanced photodetector 2, phase detector, data acquisition card.

Referring to Figure 1, the dual Mach-Zehnder heterodyne interference topology consists of 1×2 coupler 1, 1×2 coupler 2, oil-core photonic crystal fiber 1, oil-core photonic crystal fiber 2, optical circulator, acousto-optic modulator, 1×2 coupler 3, 2×2 coupler 1, 2×2 coupler 2, use 1×2 coupler 2 to divide the sensing arm led by 1×2 coupler 1 into two paths, 1×2 coupler Device 3 divides the reference arm after passing through the acousto-optic modulator into two paths, wherein after the sensing arm is divided into two paths, it passes through the oil-core photonic crystal fiber 1 and the oil-core photonic crystal fiber 2 respectively, and then divides into two paths with the reference arm Two pairs of light are combined and interfere at 2×2 coupler 1 and 2×2 coupler 2 respectively, forming a double Mach-Zehnder heterodyne interference optical path.

Referring to Figure 1, the light source controller controls the pump laser to emit pump light whose wavelength is located at the acetylene absorption line and whose light intensity is continuously sinusoidally modulated. Core photonic crystal fiber 1. The pump light interacts with the dissolved acetylene entering the core of the oil-core photonic crystal fiber 1 to stimulate the photothermal effect, causing the temperature inside the core of the oil-core photonic crystal fiber 1 to change at the continuous sinusoidal modulation frequency of the pump light. The probe light emitted by the probe laser with a wavelength at the weakest absorption point of acetylene passes through the optical isolator and 1×2 coupler 1 and enters the double Mach-Zehnder heterodyne interference optical path. When the detection light at the sensing arm passes through the oil-core photonic crystal fiber 1, since the internal temperature of the fiber is continuously sinusoidally modulated, the detection light passing through this place will cause the phase to change continuously according to the modulation frequency, while the oil-core photonic crystal 2 Since there is no pump light entering, the phase change will not be caused by the photothermal effect when the probe light enters. At this time, the two interference light signals output by the double Mach-Zehnder heterodyne interference optical path are respectively detected by the balanced photodetector 1 and the balanced photodetector After collecting by detector 2, the only difference is that the phase part of the interference signal is different. After passing through the phase detector, it will directly output two phase difference time-domain signals. Finally, the time-domain signal is collected by the data acquisition card and processed by the computer for its Fourier transform, and the signal reflecting the concentration of dissolved acetylene in the oil is obtained directly.

Referring to Fig. 2, the oil-core photonic crystal fiber 1 and the oil-core photonic crystal fiber 2 of the present invention are directly put into the oil tank of the transformer, and placed near the fault-prone parts at the same time. collected by an oil-core photonic crystal fiber. Since oil-core photonic crystal fiber 1 and oil-core photonic crystal fiber 2 are in the same position, the phase changes introduced by noise interference such as external ultrasound are the same. At this time, the phase difference time-domain signal output by the phase detector only includes the detection light passing through the oil-core photonic crystal. 1) The phase modulation signal caused by the photothermal effect can be directly obtained the concentration of dissolved acetylene in the oil after processing.

Referring to Fig. 3, the side of the oil-core photonic crystal fiber of the present invention is drilled with several micrometer-scale microholes as deep as the central core area every 10cm in the axial direction, and the diameter of the micropores is not less than 3 μm and not more than 5 μm, which allows carrying dissolved The transformer oil of acetylene molecules directly enters the central core area of the oil-core photonic crystal fiber and a small number of air holes in the cladding. The refractive index of the transformer oil in the central core area is higher than that of the cladding, which constitutes a total internal reflection mechanism of the optical fiber, and the loss of a single hole is low. More than 0.2dB, to ensure concentrated transmission of light in the fiber core with low loss, the two ends of the oil core photonic crystal fiber and ordinary single-mode fiber are fused with low loss, and the single splicing loss does not exceed 2dB, and the cladding air at both ends during splicing The holes are fused and closed to prevent transformer oil from entering the cladding air holes from the welded joints at both ends.

Referring to FIG. 3 , the photothermal interference technology of the present invention is a gas spectrum detection technology based on the photothermal effect. When there is acetylene dissolved in oil inside the oil-core photonic crystal fiber, the pump laser emits pump light at the wavelength of the P(9) absorption line of acetylene and the light intensity is modulated by a fixed frequency. The pump light and the acetylene molecule dissolved in the oil The interaction stimulates the photothermal effect. At this time, after the probe light passes through the optical fiber, the phase of the probe light will change at the same frequency. The concentration of dissolved acetylene in the oil can be obtained by detecting the phase change by interference.

Claims (6)

1. A high-reliability optical fiber detection system for dissolved acetylene in transformer oil, characterized in that it consists of a light source module, a dissolved gas sensing module in oil, and a data demodulation module; the light source module includes a light source controller, a pump Lasers, erbium-doped fiber amplifiers, optical circulators, detection lasers, and optical isolators; the sensor module for dissolved gas in oil uses oil-core photonic crystal fibers as sensing units, and is directly built into the transformer oil tank and placed near the fault defect; the system The topology is based on the Mach-Zehnder heterodyne interference structure. A 1×2 coupler 2 is introduced into the interference sensing arm to divide the sensing arm into two paths, which pass through the oil-core photonic crystal fiber 1 and the oil-core photonic crystal fiber 2 respectively, in which the pump The pump light emitted by the laser enters the oil-core photonic crystal fiber 1 through the optical circulator, and no pump light enters the oil-core photonic crystal fiber 2. The interference reference arm is divided into two by the 1×2 coupler 3 after passing through the acousto-optic modulator. The two paths interfere with the two optical paths of the sensing arm respectively to form a double Mach-Zehnder heterodyne interference structure; the two-way interference signals obtained by the detection light through the double Mach-Zehnder heterodyne interference structure are demodulated by the data demodulation module Finally, the dissolved acetylene concentration is directly obtained; the data demodulation module includes a balanced photodetector 1, a balanced photodetector 2, a phase detector, a data acquisition card and a computer. 2. a kind of high-reliability optical fiber detection system that is used for dissolving acetylene in transformer oil according to claim 1 is characterized in that, utilizes dual Mach-Zender heterodyne interference topology in conjunction with a phase detector to realize dissolving acetylene detection; The Mach-Zehnder heterodyne interference topology includes two optical paths: sensing heterodyne interference and reference heterodyne interference. The two optical paths are basically the same, and the same oil-core photonic crystal fiber is used as the sensing unit, which is placed directly inside the transformer oil tank. The same area, the difference is that the pump light enters the oil-core photonic crystal fiber 1 through the optical circulator and interacts with the dissolved acetylene inside the fiber core to excite the photothermal effect to generate a phase modulation signal, while the oil-core photonic crystal fiber 2 does not enter the pump light ; The two-way interference signal passes through the phase detector to directly obtain the phase difference time-domain signal containing only the information of the dissolved acetylene concentration. 3. A high-reliability optical fiber detection system for dissolving acetylene in transformer oil according to claim 1, wherein the frequency shift of the acousto-optic modulator is not less than 100MHz, and is used to modulate the phase modulation signal to high frequency. 4. A high-reliability optical fiber detection system for dissolving acetylene in transformer oil according to claim 1, wherein the pump laser is controlled by a light source controller to emit a wavelength of 1530.37nm and an average power of not less than 5mW continuous sinusoidal modulation light, the light intensity modulation frequency is not lower than 20kHz; the detection laser emits continuous light with a wavelength of 1550nm and power not lower than 20mW. 5. A kind of high-reliability optical fiber detection system for dissolving acetylene in transformer oil according to claim 1, is characterized in that, the optical wavelength range that can be amplified by the erbium-doped fiber amplifier is 1500nm～1670nm, and the saturated output power is less than It is lower than 20dBm, the maximum gain multiple is not lower than 30dB, and the amplifier works in automatic gain control mode to ensure that the pump light power input into the oil-core photonic crystal fiber after amplification is not lower than 90mW. 6. A high-reliability optical fiber detection system for acetylene dissolved in transformer oil according to claim 1, wherein the bandwidth of the phase detector is not less than 500MHz.

Images