Distributed magnetic field measurement on stator winding heads of a 300 MVA water turbine motor-generator using fiber-optical magnetic field sensors

Abstract:
A novel fiber optical magnetic field sensor has been developed, based on the theory of an optical strain measurement using Fiber Bragg gratings (FBG). A silica glass fiber is glued to a magnetostrictive material, which is changing its geometric shape when exposed to a magnetic field. An elongation of the magnetostrictive material affects an expansion of the fiber Bragg grating and consequently a wavelength shift of the reflected Bragg peak. This sensor was used to measure the magnetic field around the stator bars due to the current flow, and to detect the stray magnetic field of the rotor. Before that laboratory measurements were made to verify the sensor system and to characterize the system limits.