The voltage V across the magnetizing branch of the transformer during the fault is
reduced only by 20% or so during the fault, so the switching that occurs does not create a large
transformer transient. Moreover, the flux at the moment of switching is in the right direction,
not in the opposing direction as we usually assume for worst-case system transformer switching.
Another important factor is that the fault current interruption is achieved at the current zero,
at which time the voltage is maximum and the flux is zero, thereby giving no exciting current
transient.