Desenvolvimento e aplicações de sensores a fibra ótica para instrumentação de máquinas elétricas

Abstract

This thesis presents new methods for monitoring temperature and dynamic deformation in rotating electrical machines using two optical fiber sensors: 1) a smart fiber Bragg grating (FBG) sensor encapsulated in carbon fiber reinforced polymer (CFRP) and 2) a sensor based on distributed temperature sensing (DTS). In electrical machines, high temperatures and excessive vibrations, if not detected early, can wear out the electrical insulation, increasing the risk of shortcircuit failures in stator coils. This thesis is a collection of four published papers: the first two deal with sensors based on FBG, and the last two with sensors based on DTS. Because sensors are mechanically fragile to shear stresses, CFRP encapsulations provide them robustness without significantly altering their sensitivity. The first FBG sensor was built in the shape of the stator core of a three-phase induction motor (TIM) , and this design was patented. The dynamics of the motor operating with new and damaged bearings at no load and rated load were evaluated in an industrial environment. The second FBG sensor was designed to operate in contact with the bearing. In addition to allowing quick installation, the detection of defects focuses on the measuring. In the analysis of bearing defects, the test results were consistent with the theoretical results for both the FBG sensors. The third article aimed to monitor the temperature using a DTS sensor in the end-winding region of the stator bar of a 355 MW generator that overheats and has dimensions smaller than 50 cm. However, the optical interrogator of the DTS sensor does not accurately detect signals with spatial resolution below 1 m. To overcome this problem, a signal reconstruction algorithm based on signal deconvolution by total variation was used to improve the spatial resolution up to 15 cm. The fourth article focused on the thermal mapping of a 20 hp TIM operating in the paper-manufacturing industry. The DTS instrumentation is performed in all stator core slots with optical fiber coated with Teflon ® 900 𝜇m, to identify hot regions. The results achieved in the works demonstrated the potential of the proposed methods for the continuous monitoring of temperature and dynamic deformation in electrical machines.