Investment restrictions on large centralized power plants and technical and economic problems associated with the transfer of large volumes of power over long distances have led to the expansion of distributed resources in the world's electricity grids. Due to the many technical, economic and environmental benefits of distributed resources, in recent years the policies and plans of the Ministry of Energy, Regional Electricity Companies and Distribution Companies have been focused on the development of these resources. For this purpose, the objectives defined in this project are to determine the optimal location and capacity of distributed resources in the 20 kV buses of the sub-transmission substations in Isfahan Regional Electricity Company. Regarding to the location of distributed resources in the problem at the boundary between distribution and sub-transmission networks, the positive and negative effects of the addition of distributed resources will mainly be attributed to sub-transmission and transmission networks. For this reason, the objective functions defined in the optimal planning problem are aimed at maximizing the benefits for Isfahan Regional Electricity by improving the performance indicators of the sub-transmission and transmission networks under the management of the company. The definition of the problem is based on a new perspective on distributed resource planning. In this perspective, the installation of distributed resources is performed to improve the performance of high voltage networks. In addition, given that distributed resources belong to private sector investors, it is necessary to allocate the maximum possible capacity for distributed resources to 20 kV buses without imposing to Electricity Company such costs as replacing the breakers or protective systems by installing these resources. Depending on the objectives defined, the planning problem includes the objective functions, constraints and decision variables is defined and is solved for Isfahan Regional Electricity Network. The profits of reducing network energy loss and the release of capacity of transmission and sub-transmission lines and transformers are the most important components of the objective function of the planning problem. Subsequently, this planning model was also modified for distributed resources installed on 20 kV feeders and the associated planning model was implemented on a 20 kV sample feeder. In addition, a distributed resources planning model for circular distribution networks that are future networks in smart grids is presented. Its objective function, in addition to network performance indicators, also is composed of the indicators related to the operation of over current directional protection and anti-islanding protection. This model is also implemented for a test network and its results are discussed. Keywords: Distributed resources planning problem, Isfahan Regional Electricity, Anti-islanding protection, Technical and economic objective function, Sub-transmission and transmission systems.