KEYWORDS: Absorption, Signal to noise ratio, Absorbance, Signal detection, Laser applications, Signal processing, Signal generators, Signal attenuation
The corresponding experimental system was designed, and the direct absorption technology based on the principle of tunable laser absorption spectrum of inter-band cascade laser (ICL) was used to detect low concentration of sulfur fluoride (SO2F2) gas. The position of 3619 nm is chosen as the measurement spectrum line of SO2F2 gas, which can effectively avoid the cross interference of background components. At 35 ℃ of working temperature and 80 mA of current, the inter-band cascade laser emission wavelength can completely cover the absorption spectrum line at 3619 nm at the center of SO2F2 gas. The direct absorption spectrum of SO2F2 gas after deducting the background absorption is obtained by taking the logarithm of the ratio of the transmitted light intensity to the incident light intensity and the time-frequency conversion of the horizontal axis. The results show that the linear relationship between gas concentration and absorption intensity is good, the fitting coefficient R 2 is 0.997, and the system responsiveness is 0.782 mV/ppm. Three hundred sets of data were collected for 50 min, the relative standard deviation (RSD) was 0.25%, and the system sensitivity was 3.94 ppm. This method can provide a new method for the optical detection of SO2F2 gas, and then provide a reliable experimental basis for the detection of SO2F2 concentration of SF6 decomposition product in GIS gas chamber.
SO2F2 gas is one of the important decomposition products of SF6 in the GIS gas chamber. Based on the analysis of the chemical composition of the gas, the failure prediction of high-voltage electrical equipment can be realized. The SO2F2 gas detection system in the GIS is built based on the second harmonic absorption technology with an inter-band cascade laser with a center wavelength of 3599 nm. The experimental results of the tuning characteristics of the ICL laser show that when the laser works at 35°C and the drive current is 60~100 mA, the emission wavelength of the laser output can cover the wavelength range of 3615.4 nm to 3623.4 nm, which meets the detection requirements of SO2F2 gas at 3619.3 nm. The second harmonic detection results show that the gas harmonic absorption intensity increases with the increase of gas concentration, and the fitted linear correlation R2 is 0.99563, which has a good positive correlation. Collect 300 sets of data, the collection time is 50 minutes, the relative standard deviation (RSD) is 0.29%, and the system detection limit is 357.56 ppb. This method can provide a new method for the optical detection of SO2F2 gas.
Perfluoroisobutyronitrile (C4F7N) has the potential to replace SF6 due to its excellent environmentally friendly dielectric properties, and has received extensive attention at home and abroad. C4F7N has a low liquefaction temperature, so it is necessary to mix it with low-boiling gas during application. Among them, the C4F7N/CO2 mixed gas has excellent performance, but the insulation capacity is closely related to the C4F7N content. Therefore, the preparation of high-precision C4F7N/CO2 mixed gas is conducive to scientific demonstration of C4F7N and minimizes the hidden dangers of industrial applications. Through the Fourier infrared detection platform, the infrared absorption information of C4F7N gas in the 500~4500cm-1 band was obtained, and the 1200~1300cm-1 band was determined as the key research object. A portable detection system for C4F7N/CO2 mixed gas is designed based on NDIR technology. As for the C4F7N gas sensor module, the low-power EMIRS50-AT06V standard blackbody light source with rugged MEMS design and the dual-channel detector with InfraTec LRM-202 narrow bandpass filter, combined with the gold-plated gas chamber structure of the reentrant light path, can effectively improve the detection accuracy of the system.Determine the inversion algorithm of the difference principle, and finally realize the fast detection of the C4F7N gas content. The experimental results show that the non-linear correlation between SB/SA (the ratio of the amplitude of the reference signal and the signal amplitude of the measurement channel) and the volume concentration fitting nonlinearity R2 is 0.99797. Within the range of the sensor, the maximum indication error is 1.05%, and the RSD of the sensor repeatability experiment is 0.47%, 0.36%, 0.31%, 0.34%, all of which do not exceed 0.5%, indicating that the sensor has good accuracy and consistency.The high integration and portability of the system can provide a novel method for the rapid online detection of the C4F7N/CO2 mixed gas mixture ratio of high-voltage electrical equipment.
H2S and moisture content are important indicators to evaluate the potential faults and insulation performance of H2S electrical appliances. Currently, there is no report on the simultaneous detection of H2S gas and moisture content. In order to realize the accurate detection of H2S gas and H2O at the same time, Lorentz simulation analysis was performed on the absorption spectra of H2S gas and H2O molecules. The absorption was strongest near 2684nm, and there was no cross interference of SF6 other decomposition products. H2S and moisture content at different concentrations were measured by TDLAS technology in a customized CW-DFB laser with a central wavelength of 2.68μm combined with a small-volume Herriott long-range cell with multiple reflections. In order to verify the detection ability of selected spectral lines to H2S gas and H2O molecules at low concentration, trace H2S and H2O vapor with SF6 as background were detected by direct absorption technology and wavelength modulation technology respectively. In the second harmonic absorption, the minimum detection lower limit of H2S and H2O is 9.01×10-6 and 4.54×10-6, respectively. The maximum harmonic signal amplitude has a good linear correlation with concentration, and the linear fitting degree R2 is 0.978 and 0.997, respectively. SF6 gas displacement experiments with different flow rates showed that the equilibrium time of H2S and moisture content at 708mL/min was 90s and 100s, respectively. The response time of H2S and H2O at the same concentration and injection velocity is 30s and 45s, respectively. Wavelength modulation technology can provide a reliable experimental basis for the simultaneous detection of trace H2S and H2O in high voltage combination electrical appliances.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.