  Power systems normally operate at their stable operating conditions where the
power supply and demand are balanced. In emergency situations, the operators
proceed to cut a suitable amount of loads to rebalance the supply-demand and
hopefully stabilize the system. This traditional emergency control scheme
results in interrupted service with severely economic damages to customers. In
order to provide seamless electricity service to customers, this paper proposes
a viable alternative for traditional remedial controls of power grids by
exploiting the plentiful transmission facilities. In particular, we consider
two emergency control schemes involving adjustment of the susceptance of a
number of selected transmission lines to drive either fault-on dynamics or
post-fault dynamics, and thereby stabilize the system under emergency
situations. The corresponding emergency control problems will be formulated and
partly solved in some specific cases. Simple numerical simulation will be used
to illustrate the concept of this paper.
