Distributed fiber-optic sensor for real-time monitoring of energized transformer cores

Real-time temperature mapping is important to offer an optimized thermal design of efficient power transformers by solving local overheating problems. In addition, internal temperature monitoring of power transformers in operation can be leveraged for asset monitoring applications targeted at fault detection to enable condition based maintenance programs. However transformers present a variety of challenging environments such as high levels of electromagnetic interference and limited space for conventional sensing systems to operate. Immersion of some power transformers within insulation oils for thermal management during operation and the presence of relatively large and time varying electrical and magnetic fields in some cases also make sensing and measurement technologies that require electrical wires or active power at the sensing location highly undesirable. In this work, we investigate the dynamic thermal response of standard single-mode optical fiber instrumented on a compact transformer core by using an optical frequency-domain reflectometry scheme, and the spatially resolved on-line monitoring of transformer core temperature rise has been successfully demonstrated. It is found that spectral shifts of the fiber-optic sensor induced by the temperature rises are strongly related to the locations inside the transformer as would be expected. Correlation between thermal behavior of the transformer core as derived from standard IR-based thermal imaging cameras and fiber-optic sensing results is also discussed. The proposed method can easily be extended to cover situations in which high accuracy and high spatial resolution thermal surveillance are required, and offers the potential for unprecedented optimization of magnetic core designs for power transformer applications as well as a novel approach to power transformer asset monitoring.