High-Sensitivity Fiber-Optic Sensor for Hydrogen Detection in Gas and Transformer Oil

This paper reports on the characterization of a palladium (Pd)-based fiber-optic hydrogen (H
₂
) sensor for health monitoring of distribution and power transformers in the electrical grid. The sensor consists of a Pd foil, which expands due to H
₂
absorption, and a fiber Bragg grating that measures this expansion. Fifteen sensors were manufactured and characterized in gas and oil environments at various H
₂
concentrations and temperatures. In gas, the sensors were evaluated at 60 °C, 75 °C, 90 °C, 105 °C, and 120 °C and H
₂
concentrations from 0.01% to 5%. In oil, the same sensors were evaluated at 90 °C and dissolved H2 concentrations from 5 to 2700 ppm. Furthermore, the influence of carbon monoxide (CO), which is often present in transformers and can impact H
₂
response of the sensor, was investigated. At 90 °C in gas, the response to 0.01% and 5% H
₂
was on average 28 and 719 pm, respectively. At 90 °C in oil, the response to 5 and 2700 ppm dissolved H
₂
was on average 11 and 763 pm, respectively. The average, relative accuracy is better than 20% over the whole measurement range in gas and for measurements above 100 ppm in oil. These specifications make the sensor a promising candidate for online monitoring of H
₂
in transformers.