The Effect of Different Core Materials on Transformer Inrush Currents

The inrush current is one of the most common low-frequency transients, and is crucial for transformer studies and design. Core materials have an impact on the inrush current of transformers due to their different magnetizing characteristics. However, how their differences affect inrush currents and the influence level need to be further studied. In this paper, the effect of core materials, namely, the grain-oriented silicon steel, grain non-oriented silicon steel, amorphous alloy and nanocrystalline alloy, on inrush currents of transformers is investigated. Experiments are carried out to compare the inrush current peak values of these four transformers. An improved π model considering the detailed saturation process of the core is proposed for inrush current simulations on the ATP-EMTP platform. The simulated and experimental waveforms show good agreement from the peak value and wave-shape point of view. Results show that the amorphous alloy and nanocrystalline alloy transformers generate much higher inrush currents than those of the non-oriented silicon steel and oriented silicon steel transformers, and the reason is discussed in detail.