A Linear Capacitive Sensor for ppm Moisture Measurement in SF₆ Gas-Insulated Switchgear

Moisture measurement and control is very essential for gas-insulated switchgear (GIS). For safe and reliable operation, the moisture inside GIS needs to be kept within the prescribed limit. This article presents a capacitive sensor for traces of moisture measurement in SF6 gas used in GIS. The sensor is fabricated using fluorine-doped tin oxide (FTO) glass as the base substrate and silver as the upper electrode. A thin film of porous alumina (Al2O3) is used as a sensing layer for detecting the presence of moisture at parts-per-million (ppm) scale. The performance of the presented sensor is experimentally validated for different moisture concentrations in SF6 gas. The sensor shows a good sensitivity (0.238 pF/ppm) with linear characteristics (±2.05%) over the moisture range of 246-725 ppm. The response of the fabricated sensor is very accurate (±0.84%), with low hysteresis (±0.32%) and highly repeatable (±0.013%). All the data of the fabricated sensor are obtained experimentally that validate its use for an effective moisture measurement in GIS where the live conductors and other electrical equipment are surrounded by SF6 gas. The cost-effectiveness of the sensor is ensured because of its simple fabrication process and robust design.