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

Abstract

This paper reports on the characterization of a palladium (Pd)-based fiber-optic hydrogen (H2) sensor for health monitoring of distribution and power transformers in the electrical grid. The sensor consists of a Pd foil, which expands due to H2 absorption, and a fiber Bragg grating that measures this expansion. Fifteen sensors were manufactured and characterized in gas and oil environments at various H2 concentrations and temperatures. In gas, the sensors were evaluated at 60 °C, 75 °C, 90 °C, 105 °C, and 120 °C and H2 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 H2 response of the sensor, was investigated. At 90 °C in gas, the response to 0.01% and 5% H2 was on average 28 and 719 pm, respectively. At 90 °C in oil, the response to 5 and 2700 ppm dissolved H2 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 H2 in transformers.