Application of parallel paths in transmission open access

Transmission modeling--an important planning and operations activity--determines the feasibility and economic benefits of proposed wheeling, capacity expansion, and siting alternatives. A methodology is proposed to improve transaction modeling, and associated expense estimation, by applying a transmission constraint data reduction technique and a novel transmission model formulation. Various transmission modeling approaches are discussed, and a system is then selected to illustrate how a data reduction technique reduces the number of required transmission constraints, while preserving acceptable parallel path modeling characteristics. Data reduction results demonstrated in this study show that the method strongly correlates with classic network reduction objectives. The aggregation method can be used to analytically choose recommended equivalent area buses on the basis of interarea tie-line flow impacts, thereby eliminating typical ad hoc bus selection. A linear programming model is described, which represents parallel flows and manages transaction tagging and accounting to improve model optimality. The modeling framework is a large-scale approach that provides screening results to initiate detailed small-scale investigations. The methodology also supplements the flow-based transmission modeling philosophy currently under consideration by the North American Electric Reliability Council (NERC). The proposed method extends the NERC utility-level model to a subarea-level network model to improve overall transmission modeling detail and performance. In addition, the model merges an optimizing technique with the parallel path and energy tagging features into one homogeneous model. The proposed model formulation offers several significant benefits over conventional formulations. First, moving the level of network aggregation closer to the bus level improves the characterization of network parallel flows. Second, energy tagging is supported at the network subarea level, so that both area-to-area and subarea-to-subarea transactions can be tagged. Third, the model supports accurate estimation of net line flows that enable improved line loss and cost accounting. To demonstrate modeling performance, several scenarios, which simulated generation siting and overloaded transmission line conditions, were used. Model transmission line flow results were compared with AC load flow results and demonstrated encouraging results. This model, which applied aggregated intraarea generator shift factors, showed significant improvements in line flow accuracy over the traditional contract path formulation.