I have a (radial) system with several multi-winding transformers, for instance one 24 MVA 7-winding transformer from 11 kV to 1.92 kV.
I want to calculate what the short circuit current will be on the primary side, if a 3-phase or a line-line fault occur below one of the secondary windings?
For a two-winding transformer, this is quite straight forward.
However, I don't know what values to use in the multi-winding case. The capacity of each of the 6 secondary windings are 4 MVA. My intuition tells me the secondary winding will be the limiting factor.
Assuming the short circuit capacity is 100 MVA, and the transformer impedance is 10%, what will the short circuit current be?
There will be no contribution from the other secondary windings.
I would think the capacity of the secondary winding (4 MVA) is dimensioning, and therefore calculate it this way: (3 phase fault)
\$ Ik'' = 100MVA \cdot\$ \$ 4MVA / 0.1 \over \sqrt3 \cdot (100MVA + 4MVA / 0.1)\cdot 11 kV\$ = \$ 1.5 kA \$
But it could also be the primary (24 MVA):
\$ Ik'' = 100MVA \cdot\$ \$ 24MVA / 0.1 \over \sqrt3 \cdot (100MVA + 24MVA / 0.1)\cdot 11 kV\$ = \$ 3.7 kA \$
But then again: It might be something completely different, since a 7-winding transformer is quite different from a 2-winding. Any views on this? Any literature maybe?
Not of any relevance: Vector group: Yd11y0d11.20d0.20d11.40d0.40