Linear index definition to evaluate the risk of voltage collapse in a complex network

When dealing with electric systems, planning and operation, it is necessary to focus the attention on the problem of security. This is crucial especially when the electricity markets force towards a higher and higher exploitation of the network facilities to improve the business. In particular, the contingency analysis is a fundamental part of the security assessment: several techniques have been implemented in the past to study the impact of such perturbations. In this article, second order information derived from the singular value analysis of the power flow (PF) Jacobian matrix is used to obtain an effective ranking of contingencies with particular respect to the voltage/reactive problems. Besides, a quantification of the risk associated to each contingency is the output of a procedure that evaluates quasi-linear indices useful in both planning and operation.