Optimal seasonal scheduling of natural gas units in a hydro-thermal power system

The paper describes an approach for solving the seasonal operations planning problem of a hydro-thermal system where part of the thermal capacity consists of energy constrained natural gas units. Gas volume available as well as limitations on its use during the year is regulated through import contracts. Two different types of contract are modelled. One where a yearly import volume is fixed and another where a lower bound on the yearly import is fixed. The proposed planning model is intended for economic evaluation of different natural gas import contracts. The problem is decomposed into two parts. One part performs a traditional production costing given a gas schedule. The other part makes use of weekly marginal costs with first order information from the production costing algorithm in order to schedule the gas and in the case of the second type of contract, to decide on how much gas to import. The optimization method used to schedule the gas makes use of an efficient algorithm for solving this type of nonlinear problem