Improvement Of Loadability In Distribution System Using Genetic Algorithm

Abstract

Generally during recent decades due to development of power systems, methods for delivering electrical energy to consumers, and because of voltage variations is a very important problem ,the power plants follow this criteria. The good solution for improving transfer and distribution of electrical power majority of consumers prefer to use energy near loads .So small units that are connected to distribution system named Decentralized or Dispersed Generation. Deregulated in power industry and development of renewable energies are most important factors in developing this type of electricity generation. Today DG has a key role in electrical distribution systems. For example we can refer to improving reliability indices, improvement of stability and reduction of losses in power system. One of key problems in using DG’s, is allocation of these sources in distribution networks. Load ability in distribution systems and its improvement has an effective role in operation of power systems. However, placement of distributed generation sources in order to improve distribution system load ability index was not considered, we show DG placement and allocation with genetic algorithm optimization method maximize load ability of power systems .This method implemented on IEEE Standard bench marks. The results show effectiveness of proposed algorithm .Another benefits of DG in selected positions are also studied and compared. KeywordsVoltage Profile, Electric Power Losses, Distributed Generation (DG), Distribution System. 1-INTRODUCTION As predicted distributed generation will have a growing role in future of power systems, and also in recent years, this role has been slowly increasing [1]. Atomic Energy Agency (IAEA), offers following definition for distributed generation: The units of generation that give service to customer in place[2]. Council on Large Electric Systems(CIGRE), offers following definition for distributed generation[1]: Advanced Computing: An International Journal ( ACIJ ), Vol.3, No.3, May 2012 2 1 -Not to be planned centrally 2 Not to be transferred centrally 3Usually is connected to distribution network 4 Capacity between 50 to100 MW However, best definition for DG is, the source of electric energy is connected to distribution networks or directly to consumer side. The nominal amounts of these generations varied, but usually their generation capacity range from a few KW to 10 MW. These units are in substations and in distribution feeders, near loads. The effects of DG on voltage profile, line losses, short circuit current, amount of harmonic injection, stability and reliability of network before installation should be evaluated. DG placement and size are very important, because it’s non-optimal installation increases losses and rises costs. Therefore to considering above items and consumption patterns application of an efficient and powerful optimization method is a suitable solution for system planning engineering. 2APPROACH TO QUANTIFY THE BENEFITS OF DG In order to evaluate and quantify benefits of distributed generation, suitable mathematical models must be employed along with distribution system models and power flow calculations to arrive at indices of benefits. Among many benefits three major ones are considered: Voltage profile improvement, line loss reduction and line transmission apparent power improvement index. 2-1-LINE LOSS REDUCTION INDEX (LLRI) Another major benefit offered by installation of DG is reduction in electrical line losses [3]. By installing DG, line currents can be reduced, thus helping reduce electrical line losses. The proposed line loss reduction index (LLRI) is defined as: (1) Where, is total line losses in system with employment of DG and is total line losses in system without DG and it can be: (2) Where, Ii is per unit line current in distribution line i with employment of DG, Ri is line resistance (pu/km), Di is distribution line length (km), and M is number of lines in system. Similarly, is expressed as: