| The conventional power distribution system has been radial in nature, characterized by a single source feeding a network of down-stream feeders. The protection scheme for a distribution system, primarily consisting of fuses and reclosers and in some cases, relays, has traditionally been designed assuming the system to be radial. The current trend and literature show that Distributed Generation (DG), is going to increase significantly in the coming years. After connecting DG, part of the distribution system may no longer be radial, which means the coordination might not hold. The effect of DG on coordination depends on the size, the type and the placement of DG. This dissertation explores the effect of high penetration of DG on protective device coordination in a power distribution system. It identifies the cases under which the coordination can be lost for different combinations of protective devices. Solutions are first sought without making significant changes in the conventional protection schemes. These solutions are evaluated in terms of operational viability. The dissertation finally suggests an adaptive protection scheme as a complete solution to the problems identified. All solutions are implemented on actual power distribution systems simulated on a digital computer and results are reported in each case.; The dissertation consists of five chapters. Chapter one gives a background of power system protection and introduces the problem. Chapter two identifies and illustrates through simulations the problems in coordination between fuses and relays due to an arbitrary penetration of DG in the distribution system. Chapter three concentrates in the same way on the coordination between a fuse and a recloser. Both these chapters offer solutions without making major changes in the system and evaluate the operational feasibility of the solutions. Chapter four describes an adaptive protection scheme as a general solution to the problem. Chapter five concludes the dissertation.; The various problems in coordination between protective devices in a distribution system in the presence of distributed generation have not been systematically identified in the available literature. Thus, the dissertation explores these problems for the first time in adequate detail. This, along with the adaptive protection scheme suggested as a solution in chapter four, is the new contribution of this research. As a part of this solution, a fault location method to locate the faulted section in a distribution system was developed. The method uses the results of the short circuit analysis and is based on Thevnin's equivalent circuit and superposition. This also is a new contribution to the available literature. |
