Power transformer demagnetization

摘要

Switching operations and direct current applied during routine testing procedures of static winding resistance measurement leave residual magnetization in the core and/or fully saturate the core of the transformer. When a magnetized power transformer is energized, it will face extremely high magnetizing currents due to the non-linear phenomenon of core saturation. The high level of inrush currents generated upon energization may affect the internal winding geometry of the transformer and also trip harmonic protection devices in the system. This paper will discuss the demagnetization of the magnetic core of power and distribution transformers. Different algorithms are applied to a variety of transformer designs and the results are validated with excitation current measurements and Sweep Frequency Response Analysis (SFRA) tests. The knowledge acquired and the best practices suggested for transformer demagnetization are summarized for practical application in the field.