Sažetak
Inrush currents are ussually caused by transformer enrgization. Since the magnetizing branch representing the core appears as a shunt element in the transformer equivalent circuit, the magnetizing current upsets the balance between the currents at the transformer terminals, and is therefore experienced by the differential relay as a “ false” differential current. Differential relay must remain stable because tripping out during inrush conditions results in breaking a current of pure inductive nature and can be indirect cause of an internal transformer fault. Inrush currents caused by iron core saturation may reach 5-10 times the rated value when the outer winding is switched-in first, and 10-20 times the rated value when the inner winding is energized first. Such a high values increase mechanical stresses in transformer and may cause malfunction of other substation equipment. In prevention of those undesirable effects, estimation of inrush current magnitude and duration can be useful. This paper presents simulation of 300 MVA transformer energization in substation 400/110 kV “ Ernestinovo” using ATP-EMTP software.
Ključne riječi
Transformer energization inrush transients residual flux computer simulation overcurrent relay protection
