Relevance of magnetostatic forces for transformer core vibrations

Recently, increased attempts are made to attain a better understanding of transformer core noise which is generated by core vibrations. A base value of noise results from magnetostriction. However, a second mechanism is given by magnetic forces which arise throughout the core. From recent work on model cores, we conclude that a predominant role is given by interlaminar forces which cause primary sources of vibrations due to statistically distributed freedom of sheet ends. Through propagation, these inner sources contribute to vibration patterns of all surface points of the core. With effective clamping, multi-step-lap assembling of joints reduces the resulting noise levels, even if air gaps exist in overlap regions of the joints.