Magnetostriction Assessment with Strain Gauges and Fiber Bragg Gratings

Abstract

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.

Experimental comparison of localised magnetostriction difference under sinusoidal and PWM excitations

“…Each of these values is at a fundamental frequency. As we mentioned in the reference work above [8,9,22], it is seen that the strain values in the PWM excitation state are much higher than in the sinusoidal excitation state. The most important point to be considered is that to accommodate sensors above and below same points on the test lamination, air gaps are created in the transformer core in the inter-lamination regions.…”

“…Despite this, It is preferred in the measurements to be made in the localized and inter-laminations in terms of ease of use and not being affected by temperature. [4,[7][8][9].…”

“…Another issue is the excitation voltage applied during the operation. Studies carried out so far have generally been conducted using sinusoidal voltage [4,[9][10][11][12][13][14]. These studies are only cover works where measurements are made using strain gauges.…”