Vibration Reduction of Power Transformer Core.

Abstract

Recently, demand has increased for low-noise power transformers as well as large-capacity and small-size power transformers. To reduce transformer noise, it is necessary to reduce vibration of their iron cores, which is caused by magnetostrictive forces of silicon iron sheets. In this paper, a method for calculating core vibration was introduced and techniques for reducing the vibration were investigated. First, magnitudes and phases of higher-harmonic components of the magnetostriction were clarified. Then, a calculation method of core vibration using analytical solutions for a uniform beam was introduced. Calculated values for natural frequencies agreed with measured ones within 5%. Also, the vibration characteristics of a single-phase two-legged core, a three-phase three-legged core, and a three-phase five-legged core were clarified. Finally, it was found that the participation factors of magnetostriction in various portions of the core had different values for the displacement of core, and that arbitrary vibration modes could be eliminated by adjusting the magnetostriction values. Optimum combinations of magnetostriction which reduce core vibration were obtained. The preferable ratios for dimensions such as the ratio of the sectional areas of the core and yoke, or the ratio of the area moments of the inertia of the core and yoke, were proposed. In many cases, it was found that participation factors of magnetostriction in yokes were larger than those of legs, although the yokes were shorter than the legs.