Moisture Detection with Optical Methods

The detection of moisture in transformer oil is still gaining importance with regard to the state‐based maintenance of oil‐immersed transformers. This chapter provides a comprehensive outline and status quo of optical moisture sensing techniques, broadly categorized as fiber Bragg gratings (FBGs), evanescent wave (mainly micro/nano fiber (MNF)), and Fabry–Perot interferometric‐based sensors. Nowadays, the detection of moisture in transformer oil can be mainly categorized as offline detection and online detection types. The objective is to develop an FBG‐based sensor that is specifically target moisture. Based on the establishment of the evanescent wave, which is mainly based on MNF, its distribution is strongly related to the refractive index, which has a relationship with the moisture content. The Fabry–Perot interferometer is another important component in optical sensing, which can also be used for moisture content detection and measurement.