This research introduces the expected security-cost optimal power flow (ESCOPF) model. The ESCOPF problem is the standard optimal power flow (OPF) problem, but also includes the costs of the system operating within operational limits in post-contingency states as part of the total cost to minimize. Redispatch of the power system in the post-contingency state, given that the system has been operating at a given pre-contingency state prior to the contingency, yields a new total cost of system operation, which is considered the security cost of the particular contingency as a function of the pre-contingency state. The security cost is then included in the objective function. In other words, the ESCOPF problem is the OPF problem that handles system security as an economic cost instead of as a constraint, which is what has been done in previous studies of security-constrained optimal power flow (SCOPF). In addition, after the contingency, we allow post-contingency rescheduling of generators and the ability to interrupt customer loads if necessary. However, the cost of post-contingency rescheduling, such as the interruption cost the utility must pay to the interrupted customers, must be included in the post-contingency security cost. The proposed ESCOPF problem can be solved using either a decomposition method or an integrated solution method. The proposed model has been successfully tested on 3-bus, 5-bus and IEEE 14-bus cases. The numerical results of the proposed model are used to study the values of spinning reserve and interruptible load in power systems considering system security. The marginal value of spinning reserve and the marginal value of interruptible load tell us how much the expected security cost will be reduced by the availability of another MW of spinning reserve or interruptible load.
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