In this paper, C5F10O (perfluorpentone, C5 for short) is decomposed in GIS/GIL due to the existence of insulation defects. C5F10O will produce typical decomposition gases such as CO, C3F6, CO2, C3F8, C2F6, C2F4 and CF4 under overheating conditions. The concentration of the above gases under the overheating conditions is a strong correlation series of time. It is necessary to carry out high-precision fitting for the time series obtained from the above tests. First, Gauss Chebyshev process is used to reconstruct the background value, which realizes high-precision fitting and prediction and early warning of two-dimensional nonlinear time series. At the same time, the maximum likelihood estimation of three-dimensional curved surface combined prediction model is realized. This paper first analyzes orthogonal prediction model based on the grey Markov chain Gauss Chebyshev from the mathematical model level, then analyzes the decomposition characteristics of C5F10O/CO2 under local overheating conditions and its prediction technology, and obtains the optimal ratio of new environment-friendly gas insulation, which has good guiding significance for the application of the new insulation gas to the operation, the maintenance and repair technology of the high-voltage electrical equipment.
The optical structure suitable for the on-line detection of high-voltage equipment is designed, the on-line analysis of trace decomposition gas composition of insulating gas SF6 of the high-voltage equipment is realized, and the prototype is developed. The optical noise suppression technology suitable for the field is studied, the optical path system is designed to withstand the gas pressure of high-pressure equipment, and the influence of field vibration and temperature change of the high-pressure equipment on the optical path structure is solved. The judgment threshold of expert diagnosis system is formed to predict the operation state and fault type of GIS equipment according to the changes of types and contents of typical decomposition products of the sulfur hexafluoride. The above achievements lay the theoretical foundation for realizing the on-line monitoring of the insulation status of SF6 Electrical equipment, greatly promoted the development and application of ultraviolet spectrum and non dispersive infrared optical live sensing detection technology, provided effective guarantee for the safe and stable operation of the sulfur hexafluoride electrical equipment, further improved the reliability of equipment, and ensured the ability of power grid to safely and continuously provide clean energy, ensure reliable power supply and good social benefits.
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.
HF gas is an important decomposition product of SF6 gas in Gas insulated switchgear (GIS), and is an important index to evaluate the moisture environment and potential faults of high-voltage combination appliances. Therefore, HF gas detection is of great significance. A tunable diode laser absorption spectroscopy (TDLAS) sensor based on distributed feedback laser (DFB) is used to detect HF gas in GIS gas chamber.The transmitting and receiving circuits of laser signals are designed to realize the modulation of the transmitting laser signals and the control of the laser temperature. Meanwhile, dynamic amplification and voltage tracking are carried out on the detection output signal to further improve the stability and sensitivity of the system. The different sample number corresponding harmonic amplitude index fitting results show that the saturated adsorption after second harmonic amplitude basic remains the same, reaching constant extremum, firstorder index fitting correlation coefficient R2 is 0.995, 0.996, 0.997, respectively, PVDF to sample three times after adsorption saturation, gas testing response time is 3 min, optimal performance. Analysis of adsorption mechanism in SUS304 adsorption process, electrostatic attraction plays a key role, while PVDF and PTFE materials have developed microporous structures, and Vander Waals force plays a major role. HF gas calibration experiment shows that the linear relationship between gas concentration and second harmonic amplitude is well, the fitting coefficient R2 is 0.9985, the maximum absolute error of concentration inversion is -0.83, the maximum relative error is -2%, and the lower limit of detection is 0.85 PPM. To sum up, TDLAS sensor used for HF gas detection in GIS gas chamber was designed, and the advantages of PVDF material optical path cell in adsorption time and detection accuracy were verified by experiments, and the adsorption mechanism was analyzed from the perspective of material structure.
During industrial process of gas monitoring, gas pumps are typically used for extract gas dynamically. In order to improve the response time of system, high flow rate pumps are used to draw gases under detection into the gas cell, and therefore, the airflow during monitoring has an impact on system stability. In this paper, we firstly optimize the design of absorption cell through software simulation, so as to improve the airflow stability at high flow rate. And secondly, the normalization algorithm is used to try to suppress the influence of airflow fluctuation on the stability. Finally, we built a dynamic methane measurement system, and the results of normalized and un-normalized concentrations over time were provided for comparison, respectively. The experiment results show that under the flow rate is 34L/min, the response time is 1.2s, and after normalized treatment, the stability is improved from 2.68ppm to 0.64ppm (1σ).
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