Optimal Design of Protection Schemes for Distribution Networks Including Distributed Generation

Abstract

In this work the impact of distributed generation (DG) on the performance of the distribution network has been studied so as to find optimal design of protection schemes to confront the problems come from installing these DG. As the cost of transmission and distribution is rising and the costs of DG technologies are falling, this makes it more economical to meet an increase of load by connecting DG to distribution feeders rather than expanding transmission and distribution (T&D) facilities. In recent years, distributed generation draw attention to have many studies on it because there are some advantages are met such as environmental and geographical restrictions of generation units, increasing trend of load growth in distribution systems and the necessity for constructing new power plants as its consequence and tendency toward applying clean energies and independence from fossil fuels. The distribution network topology, control and protection are designed assuming that power is flowing in one direction; from substation to loads. The connection of a distributed generator to the feeders of the distribution network can cause the power flow to be bi-directional instead of unidirectional affecting the network performance and stability in a number of ways. So, we propose a new protection scheme dividing the distribution network into zones and a computer-based relay which is installed in sub-transmission controls these zones. Risk analysis is used to optimize the number and the locations of circuit breakers on the distribution feeders. As the number of the feeders increase in the network the locations of the circuit breakers increase enormously so finding the optimal solution becomes much harder. This pushes us to the need of applying metaheuristic algorithms to find the optimal solution. First we introduce two metaheuristic algorithms; Genetic Algorithm (GA) and Cuckoo Search (CS), and explain the procedure of Genetic Algorithm. The Cuckoo Search Algorithm is explained in detail using Random Walk and Lévy Flight. Then these algorithms have been implemented on a typical Egyptian real distribution network. Their results have been presented and discussed. The study revealed that the Cuckoo Search is better than the Genetic Algorithm in solving the optimal placement of risk based protective devices in distribution networks including DGs.