Detection of SF₆ Decomposition Components H₂S and CO₂ Based on WDM and CRDS

H2S and CO2 are the SF6 decomposition components indicative of severe partial discharge (PD) faults and decomposition of organic insulation materials in partial over thermal (POT) faults, and their detection requires methods with high sensitivity and the capability for long-term online monitoring. In this article, wavelength division multiplexing (WDM) and cavity ring-down spectroscopy (CRDS) were combined to achieve the synchronous and accurate detection of H2S/CO2, which was executed by multiplexing the optical paths of two distributed feedback (DFB) lasers in the 1578/1600 nm wavelength band. To avoid instrument redundancy, a self-developed high-precision laser diode controller (LDC) board was implemented for the current and temperature modulation of dual-laser. By combining the CO2/H<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {2}}$ </tex-math></inline-formula>S wavelength band with a high absorption coefficient ratio at 1600 nm, which is less interfered with by other components, and the 1578 nm wavelength band, the sensitivity of the CO<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {2}}$ </tex-math></inline-formula> detection was improved compared with that of the single-beam CRDS system. Utilizing Allan variance analysis for system limit of detection (LoD) analysis, the system achieves a LoD of 0.02/0.31 ppmv (volume fraction <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 10^{\text {-6}}$ </tex-math></inline-formula>) for H2S/CO2 within 28 s. Compared to existing absorption spectroscopy techniques, the detection error of the system for H2S/CO2 is 3.4%/2.4%, with both sensitivity and time efficiency at an advantageous level.