Study of methods for detecting inrush current in power transformers

Power transformer As one of the most expensive and vital elements of the power system it requires accurate fast and reliable protection in all transformer operating conditions. The differential protection design is used as the main protection in all transformers. One of the problems in the proper functioning of this protection is the issue of intrusion current. The inrush current often flows when the transformer is initially energized or the transformer returns to the mains after the short-circuit fault in the primary head has been rectified. The amplitude of this current is up to ten times the rated current of the transformer and can be mistaken for fault current by differential relays. Issuing a trip command in this situation will prevent the transformer from starting. Since the attack current gradually dampens over ten cycles and decreases to its nominal value it does not damage the transformer so it is necessary to use a design in the differential protection system to prevent this current from other transient currents. Detected and prevent relays from operating. Because inrush currents are perharmonic currents and especially the second harmonic amplitude is significant in