Hot-Spot Dynamic Temperature Rise of Oil-Immersed Transformer Through FBG-Based Multipoint Sensing System

The hot-spot temperature rise in oil-immersed transformers directly influences the transformer’s load capacity and thermal aging rate. However, accurately measuring hot-spot temperature rise using optical fiber sensors presents a significant engineering challenge, given the transformer’s load fluctuations, complex internal oil flow disturbances, and stress variations. In this article, we propose a multipoint sensing system based on FBGs to accurately measure the location and temperature increase of winding hot spots under variable operating conditions. Specifically, two stress-insensitive FBG temperature sensors, made entirely of dielectric materials, are designed and fabricated, demonstrating a linearity of 0.99%–1.65%, a repeatability of 1.07%–1.45%, and a response time of approximately 10 s. To build a comprehensive monitoring system, multiple FBG temperature sensors are installed on the iron-core surface, within the windings, and in the vertical oil channel. During the temperature rise test, the spatial and temporal variations of temperature inside the transformer are obtained. The hot-spot winding temperature rise reaches $62.9~^{\circ } $ C, and the top oil temperature rise is $39.6~^{\circ } $ C. The steady-state hot spot is concentrated in the 10th-to-12th sections of the winding. The system achieves 65-mm spatial resolution vertically and is enhanced to 30 mm in critical hot spots. This study grasps the dynamic temperature rise rule of oil-immersed transformer hot spots under load fluctuations, providing data support for optimizing the transformer’s internal structure and regulating its load.