Improvement of Loadability in Distribution System Using Genetic Algorithm

Generally during recent decades due to development of power systems, the 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 the majority of consumers prefer to use energy near the loads .So small units that are connected to distribution system named "Decentralized Generation" or "Dispersed Generation". Deregulated in power industry and development of renewable energies are the 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 the 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 the operation of power systems. However, placement of distributed generation sources in order to improve the 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 the IEEE Standard bench marks. The results show the effectiveness of the 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 the distributed generation will have a growing role in the future of the power systems, and also in recent years, this role has been slowly increasing [1]. "International Atomic Energy Agency" (IAEA), offers following definition for distributed generation: The units of generation that give service to the customer in the place[2]. "International 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 the distribution network 4 Capacity between 50 to100 MW However, the best definition for DG is, "the source of electric energy is connected to distribution networks or directly to the 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 the distribution feeders, near the loads. The effects of DG on the voltage profile, line losses, short circuit current, the amount of harmonic injection, stability and reliability of the network before installation should be evaluated. DG placement and size are very important, because it’s non-optimal installation increases the losses and rises the costs. Therefore to considering the 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 the 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 the 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 the reduction in electrical line losses [3]. By installing DG, the line currents can be reduced, thus helping reduce electrical line losses. The proposed line loss reduction index (LLRI) is defined as: (1) Where, is the total line losses in the system with the employment of DG and is the total line losses in the system without DG and it can be: (2) Where, Ii is the per unit line current in distribution line i with the employment of DG, Ri is the line resistance (pu/km), Di is the distribution line length (km), and M is the number of lines in the system. Similarly, is expressed as: