The increased use of renewable energies promotes decarbonization and raises the load on power distribution networks, forcing responsible distribution network operators to re-evaluate and re-design their networks. In this study, we focus on infrastructural decomposition, where the distribution network is decomposed into multiple parts and planning problems, which are then optimized separately. Based on empirical requirements from literature and discussions with experts, we present a novel mixed integer linear optimization model that allows to use exact solution approaches for realistic large-scale distribution networks. We perform extensive computational experiments and a sensitivity analysis to determine correlations between the values of model parameters and computation times required to solve the resulting model instances to optimality. Our Article (authors: Sascha Burmeister and Guido Schryen) has been accepted for publication in the Springer Journal Energy Systems. The authors gratefully acknowledge the financial support provided by the European Regional Development Fund (ERDF) in the framework of FlexiEnergy (project number 0801186, EU-2-1-028) and the funding of this project by computing time provided by the Paderborn Center for Parallel Computing (PC²). A preprint of the publication is available for download at the following address: https://ris.uni-paderborn.de/record/42179.