Research And Realization Of HF Gas Detection Based By Tunable Diode Laser Spectroscopy

Sulphur hexafluoride （SF₆）, which has been applied to the modern high voltageelectrical equipment such as gas insulated substation（GIS）, Gas-insulated cable（GIC）,gas insulated transformer（GIT）, etc., has excellent insulation and suppression arcperformance. However, the SF₆gas will generate harmful low-fluoride under thecondition of insulation fault, which will influence the performance of electricalequipment. The decision of latent fault in SF₆gas electrical equipment can be mademore timely and accurately through online monitoring of content change of HF, oneof SF₆gas decomposition. It is of great significance to develop HF detection devicewhich has high sensitivity, high selectivity, fast responding speed and nocross-interference for safe operation of high voltage electrical equipment.This paper does a research on HF gas detection device based on tunable diodelaser absorption spectroscopic（TDLAS） technology, which consists of three partsincluding decision of detection method and HF gas line selection, implementingdetection equipment and designing a lock-in amplifier module, system optimizationand data processing.1, Compared with each HF gas detection method, harmonic detection based onTDLAS technology was selected. Doing gas line selection of the HF （1310nm） wasbased on the following reasons, which is utilizing HITRAN spectrum library to selectspectrum line; using the fourier transform infrared spectrum（FTIR） method to scanHF gas with a wide spectrum, from which we get the accurate HF gas absorption peakposition; diode lasers emitting near-infrared radiation at wavelengths absorbed by HFgas are commercially available; there is no other gas composition interference at1310nm, and the1310nm is a low loss window in the fibre-optical communication.2, Realizing HF gas detection device based on TDLAS technology, includingselection and designation of each component. By analyzing parameters applicable toinstallation such as frequency range, harmonic number, time constant and phasedifference, the lock-in amplifier module with wide frequency range, adjustableharmonic number of1f/2f, time constant and phase difference was developedtargetedly. This paper also provided optimization of the performance and lock-in parameters fitting HF detection. This module replaced the commercial lock-inamplifier.3, Considering the particularity of the detection device, we analyzed typicalcharacteristic values, which were amplitude modulation, frequency modulation,amplitude scan, scan frequency, that impacted on typical eigenvalue of harmonicsignal including SNR and peak value as well as providing basis of selection ofmodulation parameters. By performing stability analysis of detection device andbackground signal subtraction, we suppress interference such as surplus amplitudemodulation and optical interference fringes and do concentration inversion and dataprocessing. By researching the system detection limit theory, we obtain detectionlimit after optimizing modulation parameters and realize highly sensitive detectiondevice.