Long-Term Performance of Fibre Bragg Grating Sensors for in Situ Thermal Monitoring of Random Wound Electric Machine Coils

This paper investigates the long-term performance of a Fibre Bragg Grating (FBG) sensor used for in situ thermal monitoring of random wound electric machine coils. An experiment was performed using a motorette instrumented with an FBG thermal sensing system. The motorette was energised under a standard S6 duty cycle with overloaded thermal levels to facilitate accelerated lifetime testing and to replicate the thermal conditions of electric machines. The performance of the FBG sensor was evaluated through calibrations conducted both before and after the experiments to assess changes in the transfer function and sensitivity. Additionally, FBG measurements were compared with those of a Type <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$K$</tex> thermocouple to analyse relative performance, including differences in measurements and response times. The results enhance the understanding of FBG sensor performance in electric machine environments and further highlight its potential as a promising solution for in situ thermal monitoring.