  This paper focuses on the issue of network connectedness (NC) in
security-constrained optimal transmission switching problems, which is
complicated by branch contingencies and corrective line switching. Two criteria
are firstly proposed with the principle of preserving NC as much as possible
within reasonable limits. By extending the electrical flow based NC
constraints, a proposition is derived to associate different cases of NC with
the optimum of a linear program, yielding the mathematical formulation of the
NC criteria. By Karush-Kuhn-Tucker conditions, this formulation is further
transformed into a tractable version which can be incorporated with existing
SCOTS models without affecting the applicability of original solution
approaches. Finally, case studies on various networks and SCOTS models
demonstrate the efficacy of the proposed approach.
