Probabilistic Analysis of Enhanced Transmission Feeder Ratings to Optimize Generator Unit Commitment

To reduce the energy costs imposed on customers, Con Edison is optimizing the commitment of baseload generating units. Con Edison’s transmission system is operated to an N-1-1 reliability standard, keeping sufficient resources on-line to clear loads above "normal" ratings and rebalance the system after outages. To lessen the need for these resources, Con Edison proposed to relax its procedures to require loads be cleared above 300-hour ratings rather than the lower "normal" ratings. In taking this action the principal concern is whether this would adversely affect system reliability. In this paper, we describe the less onerous dispatch policy proposed, the calculation of the savings that ensue, and a reliability assessment made using a Monte Carlo simulation of the reliability performance of the system to ascertain the consequences of the changes in dispatch. It was concluded that significant cost savings could be achieved with little impact on reliability. This has been realized in practice.