Sensitivity analysis on different types of electrical network modeling for the network constrained hydrothermal scheduling problem

The network constrained hydrothermal scheduling problem determines an optimal hourly dispatch considering line capacities and security constraints. The electrical network can be modeled either by a multi-area approach, with only interchange limits among areas, or by a detailed approach, where each individual branch is represented as a transportation model, a dc model with or without line losses, or as an ac model. This paper compares these types of representation in a real study case for the Brazilian system. We compare hydro and thermal generation, flows in system interconnections, individual line flows, and system operation costs. Numerical results suggest that a poor representation of the transmission lines and losses can lead to an insecure system dispatch related to electrical constraints. For low load levels, a dc model with line flow losses yields quite reasonable results. However, as congestion increases, the need to represent the nonlinear ac flow relations becomes apparent.