The calculation of inrush current in three-phase transformers

The inrush current associated with energising power transformers can cause interference and damage to other system components. The paper sets out to describe an accurate analytical method which can be used to find the inrush current in any 3-phase transformer in common use. The method is an extension of one previously described to calculate inrush in single-phase transformers. The method is powerful in that the current and its decay can be calculated over many cycles, not just the first peak, as has been possible by other methods. A comparison is made between different transformer connections and illustrated by numerical examples. These show, for example, that resistance in the neutral of a star connected transformer has little effect compared to using the same resistance in series with the energised windings.