Electric power systems are increasingly relying on small renewable plants that must be connected to a bulk grid. This paper proposes a strategy to solve the transmission line planning problem for such an integration. The model minimizes the costs of investment and annual energy losses, considering as planning alternatives the building of transmission lines, the collector substation allocation and the voltage magnitude levels of the transmission line while ensuring the operational constraints of the network and the voltage magnitude at connection points with the bulk power system (BPS). Linearization and approximation techniques are used to obtain an approximate mixed-integer linear programming (MILP) model from the original mixed-integer nonlinear programming model. A search-space reduction procedure is proposed to obtain the most qualified sites to accommodate collector substations. The combined strategy leads to a reduction in the computational effort, which allows full-scale studies of the optimal integration of a set of small renewable sources. For intermittent renewable sources, the proposed approach is used to obtain the Pareto front considering the total planning cost and the annual distributed energy. The results of two scenarios, using a real-world Brazilian case, certify the benefits of the proposals.