Power transformers have an imperative role in the future developments of the electrical grids. Treated as crucial assets for transportation and distribution of electrical energy, transformers are currently being studied regarding to the integration of technologies aiming to diagnose problems and monitoring data of electrical power grid. Furthermore, environmental noise pollution has gained importance, especially in active units of the power grid, located near consumers, such as transformers. Transformers noise can be classified according to its source: core, windings and cooling. This study addresses an experimental characterization of one of the main causes of transformers core noise-magnetostriction of electrical steel. An evaluation of magnetostriction properties of electrical steel, including resistive strain gauges and Fiber Bragg Gratings (FBGs) measurements with an Epstein frame, are presented and discussed. The magnetic flux density influence on hysteretic strain behavior of magnetostriction was evaluated, as well as the effect of a clamping load on core joints. Nowadays, optical interrogators for Bragg gratings have a high acquisition frequencies and wavelength sensitivity when compared to former optical interrogation systems, allowing to evaluate physical phenomena without electromagnetic interference and with equivalent resolution of conventional strain gauges.

Power transformers are associated with the radiation of unwanted noise in many circumstances due to its low frequency and relative high power, which reduction and mitigation is imperative. It is known that the main source of this noise are originated by the vibrations induced in the active part, namely the core, primarily due to electromagnetic forces and magnetomechanical effects. On the other hand, the laminated design of the core is indispensable in order to reduce the Foucault currents losses. Thus, in addition to the electrical requirements, the development of an appropriate model of the core dynamic behavior taking into account its segmented structure is urgent, in order to avoid resonances at any of the excitation frequencies. In the current proceeding, the influence of the core equivalent dynamic mechanical properties on a power transformer radiated noise was studied by performing a numerical parametric analysis. It was concluded that the active part stiffness properties, namely the directional component related to the out of lamination plane bending, ruled the vibroacoustic behavior of the transformer for the studied frequency range.