Magnetization process in electrical steel sheets

在使用电工钢板的变压器、发电机和电机中，能量损耗很大程度上取决于这些钢板中的磁区。因此，要了解损耗机制并开发降低损耗的策略，就需要通过显微成像对磁畴和磁化过程进行基础研究。然而，为了降低涡流效应，薄片上覆盖着不透明的绝缘涂层，这使得通过光学手段直接观察磁畴结构是不可能的。对于磁光克尔显微镜，必须去除这一覆盖层，并仔细抛光表面，这不幸地导致了磁性和磁畴结构的急剧变化。通过使用最近开发的新一代磁光指示膜(MOIF)，这种薄膜被放置在涂布的薄片上，并间接揭示了下面的磁区分布，这种情况已经发生了很大的变化：现在可以在绝缘涂层存在的情况下以足够的分辨率成像，甚至可以通过在工频下单次激发成像来以时间分辨的方式成像。此外，指示器膜还允许对晶界上的磁极进行成像，从而可以研究晶界对磁通传输的作用。在本项目中，将利用MOIF膜的电势来更深入地了解电工钢在工作条件下的准静态和动态磁化过程。目标是从根本上了解能源损失的微观来源，为有针对性地将电气设备和机器的损失降至最低奠定基础。

The energy losses in transformers, generators and electro-motors, where electrical steel sheets are utilized, are strongly determined by the magnetic domains in these sheets. The understanding of the loss mechanisms and the development of strategies for their reduction therefore requires fundamental studies of the domains and magnetization processes by microscopic imaging. To lower eddy current effects, however, the sheets are covered by non-transparent insulation coatings that make a direct observation of the domain structure by optical means impossible. For magneto-optical Kerr microscopy this cover layer has to be removed and the surface has to be carefully polished, which unfortunately leads to drastic changes of the magnetic properties and domain structure. By using a recently developed new generation of magneto-optical indicator films (MOIF), which are placed on top of coated sheets and which indirectly reveal the underlying domain distribution, the situation has considerably changed: the domains can now be imaged in the presence of insulation coatings with a sufficient resolution and even in a time-resolved manner by single-shot imaging at power frequencies. The indicator films furthermore allow for the imaging of magnetic poles at grain boundaries, making it possible to study the role of grain boundaries for the flux transport. In this project the potential of the MOIF films shall be used to obtain a deeper understanding of the quasistatic and dynamic magnetization processes in electrical steel under working conditions. The goal is a fundamental understanding of the microscopic sources of energy loss to provide a basis for a targeted minimization of loss in electrical devices and machines.