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 paper, we propose a multi-point sensing system based on FBGs to accurately measure the location and temperature increase of winding hot spots under variable operating conditions. Specifically, two stressinsensitive FBG temperature sensors, made entirely of dielectric materials, are designed and fabricated, demonstrating linearity of 0.99% to 1.65%, repeatability of 1.07% to 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◦C, and the top oil temperature rise is 39.6◦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 enhances to 30 mm in critical hotspots. 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.