Direct incorporation of fault level constraints in optimal power flow as a tool for network capacity analysis

The aim of this paper is to present a method for the direct incorporation of fault level constraints (FLCs) in the optimal power flow (OPF) as a tool for network capacity analysis, i.e., optimal generation expansion planning within an existing network. A mathematical methodology to convert constraints imposed by fault levels to simple nonlinear inequality constraints is developed. No new variables are introduced in the OPF formulation to describe the additional constraints. Most common OPF-solving engines already have the computational capacity to handle numerous nonlinear constraints, such as the ones described by the power balance equations on buses. Therefore, once FLCs are converted to nonlinear constraints described by OPF variables, they can be directly introduced to any optimization process performing the OPF. A 12-bus/15-line test case demonstrates the advantages of the new method in comparison with a previously proposed iterative method that converted them to restrictions on new capacity. It also proves that when FLCs are ignored, the capacity of the network to absorb new generation is overestimated.