Multiplexing FBG Thermal Sensing for Uniform/Uneven Thermal Variation Monitoring in In-service Electric Machines

This paper reports a distributed thermal sensing system for stator winding internal thermal conditions monitoring in operating low voltage electric machines (LVEMs). To achieve multiple thermal sensing points distributed circumferentially in the interior of the stator windings structure, the proposed sensing system utilises the multiplexing feature of fibre Bragg grating sensing (FBG) technology coupled with flexible and non-conductive sensing fibre packaging. The proposed technique enables distributed temperature monitoring with much reduced sensing volume, weight and wiring, including a key advantage of ease of in-situ sensing points repositioning post-installation. System performance was evaluated in tests on a purpose built inverter driven totally enclosed fan cooled induction machine (TFEC-IM). In addition, its potential use for thermal capacity monitoring and evaluation of the examined TEFC-IM design under deteriorated cooling capability is evaluated. The results demonstrate that the proposed sensing system is effective in providing circumferential peak temperatures distribution of the stator windings in operating machines under normal and abnormal operating conditions.