Embedded FBG Sensors in Carbon Fiber for Vibration and Temperature Measurement in Power Transformer Iron Core

This paper presents a new methodology for measuring vibration and temperature using fiber Bragg grating (FBG) sensors embedded in carbon fiber polymer attached directly on the iron core of a power transformer. The device has a quick-coupling clip design and is fabricated from a carbon fiber reinforced composite (CFRP) for robustness and flexibility. Temperature and vibration FBG sensors are embedded in the carbon fiber clip, which is easily and quickly coupled directly to the transformer iron core. In the low frequency ranges, from 0 to 500 Hz, vibrations are mainly generated in the core. Rigidity is controlled by clip thickness and geometry, since the system is designed to have a wide operating frequency range. The embedded strain FBG sensor sensitivity has been improved due to its spring-shaped design static and dynamic simulations applying the Finite Element Method (FEM) were performed to determine the optimal dimensions and structure of the part. The clip's frequency response function (FRF) was assessed and tested by using three techniques: FEM harmonic analysis, mechanical impact testing, and optical FBG sensing. The results demonstrate a 3.94 % differential among the methods. A comparison was made of the power transformer's FRF when fitted with a glued free FBG sensor and an embedded FBG sensor. In both cases, the transformer was subjected to varying electrical load conditions (no-load, linear, and nonlinear load). The results showed a 19 % average sensitivity improvement when the embedded sensor was compared to the free sensor.