Calculation and Analysis of Transformer Inrush Current Based on Parameters of Transformer and Operating Conditions

An inrush current is a transient current with high amplitude that may occur when a transformer is energized under no load or lightly loaded conditions. The magnitude of inrush current may be as high as ten times or more times of transformer rated current. This could result in huge mechanical and thermal stresses on transformer in addition to inadvertent operation of the protective relay systems. This paper represents the effects of some factors on the inrush current of transformers. For this purpose, a one-phase transformer is simulated in MATLAB and the effects of switching angle variation, the energizing circuit impedance and the remanent flux on the characteristics of inrush current are investigated. The results show that increasing circuit resistance or switching angle will decrease inrush current amplitude. Also, it is concluded that for reducing inrush current, appropriate switching angle with respect to the remanent flux must be selected. The results can be used for a better understanding of the inrush current characteristics and proper actions of the protective system. Ill. 7, bibl. 13, tabl. 1 (in English; abstracts in English and Lithuanian). http://dx.doi.org/10.5755/j01.eee.109.3.162