Point-on-wave switching procedure influence on power transformer differential protection performance

• PoW procedure does not jeopardize transformer differential protection reliability. • PoW procedure may improve transformer internal fault detection. • Shape of the magnetizing characteristic does not affect PoW procedure efficiency. Magnetizing inrush currents of power transformer may pose a serious threat to the transformer itself but also may jeopardize proper operation of transformer differential protection. Thus, their mitigation is a crucial issue in the electric power system and can be reached by proper transformer energization. Most of the existing Point-on-Wave (PoW) switching methods are usually tested only under ideal conditions, moreover - possible issues with their influence on the transformer differential protections operation are utterly ignored. In this paper all these questions are thoroughly analysed. The control strategies investigated in this paper can be used to completely eliminate transformer inrush currents (if residual fluxes are estimated precisely and circuit breakers scattering is negligible) for a wide range of transformer constructions and allowing for possible reduce of time delay between consecutive close commands to minimum. Operation efficiency of the considered in this paper PoW switching methods has been tested for various shapes of transformer magnetizing characteristics and under conditions when the remanent flux is not precisely known or when some circuit-breaker scattering occurs. The paper presents analysis of the PoW switching technique impact on the transformer differential protection operation and on effectiveness of various transformer inrush current restraint methods. All simulation tests have been realized in Matlab/Simulink as well as in ATP-EMTP environments.