
Fault Current Analysis 219
On the instant of fault, the stator coils get shorted and the stator current starts ris-
ing rapidly with a corresponding sudden and fast increase in the ux. However,
in reference to Figure 9.5, damper bars on the generator pole faces prevent the
sudden increase in the ux with opposing current in the damper bars, forcing the
stator ux in the air gap to take the path mostly in air as shown in Figure9.5(a). In
salient pole machines, the direct and quadrature axes (d- and q-axes) have different
magnetic structure; hence, both d- and q-axis are shown. As the damper bar current
decays exponentially in ...