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This paper describes a new procedure for the optimal long range expansion planning of a transmission network. In addition to providing an optimal plan, a set of cost competitive expansion plans can be generated. System expansion is specified in terms of discrete transmission lines and two kV levels. Economic impact of factors such as cost escalation, economy of scale, right-of-way unavailability, external system interconnections, etc., are incorporated in the formulation. A dynamic optimization procedure based on a nonlinear branch and bound algorithm is employed. The resulting optimal plan specifies when, where, and what type of construction should occur. A unique feature of the method, which reduces considerably the computational burden, is an automatic generation of alternatives algorithm and associated procedures for elimination of infeasible and non-optimal alternatives early in the process. Computational speed can also be affected by the user option of employing either dc or ac load flow calculations.