A ferroresonance circuit is established when a transformer is tripped out and isolated from the system along with the connected line. Such a condition occurs prior to the energization of the second transformer while the first transformer is
already energized. Furthermore, this condition can result from the clearance of a fault on either side of a transformer. In Figure 14, it is assumed that the fault occurs on the low-voltage side of T1, and is cleared by tripping both CB1 and CB3. Under this condition, the isolated transformer T1 is still energized through the capacitive coupling between the two-line circuits, and the ferroresonance condition can be established, Dolan, et al. (1972), Iravani (2000). The possible ferroresonance mode can be fundamental, subharmonic and chaotic.