Effectiveness of the Distribution Factor Approximations Used in Congestion Modeling

– Congestion has widespread impacts on the availability and utilization of the existing transmission systems and consequently on the operation of competitive markets in electricity. The distribution factors play a key role in the modeling of congestion in various market applications. These factors are linear approximations of sensitivities of variables with respect to various inputs and are computed for a specified network topology and parameter values. In practice, the factors are used over a wide range of system conditions. This paper investigates the analytical characteristics, the robustness and the quality of the approximations provided by key distribution factors such as injection shift factors (ISFs) and power transfer distribution factors (PTDFs). We examine the range of conditions over which these factors can provide a reliable approximation for large power system networks. The numerical simulation results indicate that the errors of the approximations stay in an acceptable range under a broad spectrum of conditions including contingencies used to establish n-1 security.