Optical fiber sensor for the continuous monitoring of hydrogen in oil

Abstract We demonstrate an optical fiber based hydrogen sensor to determine the dissolved hydrogen concentration in oil. This is of special interest in the prevention of the malfunction of power transformers, which has a significant social, economic and environmental impact. This malfunction is often related to the aging and degradation of the insulating system of the transformer. Since hydrogen is produced in most of these transformer faults, the change in hydrogen concentration is a marker for this degradation processes. We show that a PTFE–Pd-capped Mg–Ti thin film based fiber optic sensor is able to measure the dissolved hydrogen concentration quantitatively between 5–15 ppm at 21 °C, 5–30 ppm at 40 °C, 5–130 ppm at 60 °C, and 5–1500 ppm at 80 °C. Furthermore, we find that the presence of dissolved CH4 and O2 has little or no influence on the measured hydrogen pressure. Only at high concentrations we find that the oxygen adversely affects the sensor's response due to a competitive water formation reaction. Alloying the catalytic palladium layer with copper significantly improves the performance of the sensor in an oxygen-containing oil environment. Low carbon monoxide concentrations severely hamper the sensor kinetics and optical response. Therefore, protective coatings need to be developed to ensure a stable operation of these types of sensors over long periods of time.