Hydrogen evolution, identified by dissolved gas analysis (DGA), is commonly used for fault detection in oil immersed
electrical power equipment. Palladium (Pd) is often used as a sensing material due to its high hydrogen absorption
capacity and related change in physical properties. Hydrogen is absorbed by Pd causing an expansion of the lattice. The
solubility, and therefore lattice expansion, increases with increasing partial pressure of hydrogen and decreasing
temperature. As long as a phase change is avoided the expansion is reversible and can be utilized to transfer strain into a
sensing element. Fiber Bragg gratings (FBG) are a well-established optical fiber sensor (OFS), mainly used for
temperature and strain sensing. A safe, inexpensive, reliable and precise hydrogen sensor can be constructed using an
FBG strain sensor to transduce the volumetric expansion of Pd due to hydrogen absorption.
This paper reports on the development, and evaluation, of an FBG gas sensing OFS and long term measurements of
dissolved hydrogen in transformer mineral oil. We investigate the effects of Pd foil cross-section and strain transfer
between foil and fiber on the sensitivity of the OFS. Two types of Pd metal sensors were manufactured using modified
Pd foil with 20 and 100 μm thickness. The sensors were tested in transformer oil at 90°C and a hydrogen concentration
range from 20- 3200 ppm.