During first energization the transformer experiences inrush current caused by core magnetization starting from an arbitrary residual flux. This inrush can be several times the rated current for a short time and may cause protection to see high currents that are not faults. The core flux rises to its normal value and the magnetic domains align. Operators monitor voltages, currents, temperatures and gas relays closely and may take oil and gas samples to confirm that no internal fault occurred during the initial energization.