Nowadays, renewable energy resources (RERs) are greatly increasing. The intermittent characteristics of the RERs will affect the transmission network expansion planning (TNEP). Consequently, this paper presents a new problem formulation and solution procedure for the TNEP which can cope with the intermittent characteristics. Taguchi's Orthogonal Array Testing (TOAT) is used to select the scenarios which represent the loads and RERs uncertainties. In this paper, a new index “Renewable Energy Leak (REL)” is proposed to evaluate the “unutilized or leaked” renewable energy in the TNEP. For minimizing the investment cost of transmission network expansion, annual generator operation cost, and annual transmission line loss cost, the meta-heuristic Adaptive Tabu Search (ATS) algorithm is used while the system operating limits including REL index are taken into account as the optimization constraints. The proposed procedure is tested in a modified IEEE Reliability Test System 79. The results show that the proposed method is efficient and promising.