Security Constrained Unit Commitment for open markets

For many electric power systems the limitations of the transmission network strongly affect the system operation. In traditional regulated power systems, the operator follows operating rules and procedures to schedule generation so that the power system operates reliably. As the power industry moves towards open markets, it is necessary to develop power system schedules that produce high-quality nondiscriminatory schedules that are consistent with secure operation. This paper describes the Security Constrained Unit Commitment (SCUC) program that has been developed to meet this need. The SCUC program optimizes the scheduled generation and price-sensitive load while satisfying generation, reserve requirements, transmission constraints, and generator operating constraints such as minimum up and down times. The transmission constraints modeled are of two types: branch-flow constraints insuring that line and interface thermal limits are satisfied (for steady-state operating conditions) for the forecasted network configuration and for the configuration with a specified set of network and generator outages (i.e. contingencies). These constraints, which are enforced in a preventive mode, an automatically generated by the program; and import and export constraints limiting the generation from specified generators and loads. These constraints which can be used to model voltage and dynamic security constraints, are developed using offline analysis and are inputs to the program. This paper describes the methods used to develop secure schedules and describes our experience using this program