The wind turbine generation (WTG) sources are generally integrated into network in order to reduce power losses, avoid congestion, improve voltage profile and provide electricity during peak load. Appropriate sizing and sitting of WTGs play a notable role in minimization of the loss in distribution systems. In this paper, a new two-step PSO algorithm is proposed to facilitate placement of WTGs considering their maximum allowable capacity. Also, the location and maximum allowable capacity of WTGs are determined with the aim of minimizing power loss and sustaining the constraints such as bus voltage and loading of feeders in the desired range. In the proposed dual PSO algorithm, there are two steps in each iteration: the first step is implemented in determination of the WTGs optimal location as a control variable, and in the second step, the objective function value is determined among some scenarios which are generated based on the number and capacity of the WTGs, so that all constraints are satisfied. The proposed method feasibility is approved using sample 84-Bus and 32-Bus test systems. (C) 2016 Elsevier Ltd. All rights reserved.