Energization of a transformer under no load or lightly loaded conditions may result in inrush current with high amplitude that can be comparable with the fault currents. These currents have undesirable effects, including malfunction of the differential relay, mechanical and thermal stresses on transformer and reduced power quality of the system. In this paper, a sequential phase energization technique has been used to mitigate magnetizing inrush current in a grounded system. Because in this technique, the size of the resistor, which is connected to the neutral point of the transformer, has an important role, analytical formulas have been derived to calculate inrush current amplitude with a neutral resistor. These analytical formulas have been implemented in the M-File of the MATLAB software for calculation of different inrush current reduction ratio. Then for the verification of the results, the obtained neutral resistor has beenapplied to the equivalent circuit of a typical three-phase transformer and inrush current reduction has been determined by MATLAB SIMULINK. Ill. 7, bibl. 13 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.108.2.147
Simulation of Magnetizing Inrush Current of Three-Phase Three-Legged Transformers by Direct Measurement of Coils Inductance