Abstract
A compact ppb-level SO2 photoacoustic sensor was developed for the application of SF6 decomposition detection in electric power systems. The selection of the SO2 target spectrum is discussed in detail in the infrared (IR) and ultraviolet (UV) spectral regions. Based on the result of the spectrum selection, a small-sized UV-band diode-pumped solid-state laser (DPSSL) emitting at 303.6 nm with an output power of 5 mW was developed. A differential photoacoustic cell (PAC) was designed to match the output optical beam, obtain a high Q-factor and reduce the system flow noise in the SF6 buffer gas. The performance of the sensor system was assessed in terms of gas flow rate, linearity and detection sensitivity. A SO2 detection limit (1σ) of 74 ppbv was achieved with a 1-s integration time, which corresponds to a normalized noise equivalent absorption (NNEA) coefficient of 1.15 × 10−9 cm−1WHz-1/2.
Highlights
In electric power systems, sulfur hexafluoride (SF6) has been widely used as an insulating medium in gas circuit breakers (GCBs), gas-insulated switchgears (GIS), transformers (GIT), and transmission pipes (GIL) since pure SF6 gas is noninflammable and highly reliable due to its chemical inertness
We report the development of a highly sensitive SO2 photoacoustic sensor for the application of SF6 decomposition detection in an electric power system
A novel compact diode-pumped solidstate laser (DPSSL) laser emitting at 303 nm was selected
Summary
Sulfur hexafluoride (SF6) has been widely used as an insulating medium in gas circuit breakers (GCBs), gas-insulated switchgears (GIS), transformers (GIT), and transmission pipes (GIL) since pure SF6 gas is noninflammable and highly reliable due to its chemical inertness. Trace gas sensors based on laser absorption spectroscopy (LAS) techniques are widely used due to their high detection sensitivity and selectivity, their fast response time as well as their cost effectiveness [9,10,11,12,13]. In 2005, Somesfalean et al [23] used a tunable UV laser in the wavelength range between 302 nm and 303 nm with an output power of 6.9 nW for SO2 detection In this case, the detection limit was ~20 ppmv at atmospheric pressure. Several SF6 physical constants (density, thermal conductivity, molar mass, specific heat, viscosity, et al.) determine the generation of photoacoustic signal in the PAS, and strongly differ from those applicable to N2 These gas sensors are unsuitable to apply to electric power systems. The new optical source, a novel PAC design and strong target spectrum resulted in a ppb-level SO2 minimum detection limit
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