Anti-Fault Performance Evaluation And Fast Restoration Of Large Area Breakdown Of Electric Distribution Grids

In order to evaluate the strength of distribution girds and find out the critical, weak and bottle-neck parts to guid the expanding plan and and avoid large area break down of distribution systems under emergency circumstances, the following contributions have been made:A set of indexes to evaluate the anti-accident performance of distribution grids after disastrous events is proposed. The index of structural anti-fault ability identifies the strengthen of the layout. The index of security level identifies the limitation due to the capacity of power apparatus. The total anti-fault ability is defined as the product of structural anti-fault ability and the security level indices. The load varying behaviour the uncertainty of loads and the weights for different fault type are also taken into consideration.The process of anti-fault evaluation is suggested on the based of setting faults on each minimum distribution part, respectively. The sesults of the evaluation are managed into appropriate forms, which is helpful to find out the critical, weak and bottle-neck parts of distribution grid for expansion planning.Two approaches of distribution network reconfiguration with the least shaded loads are presented. One of them is a heuristic approach mainly including independent tripping operation identification and the least load shadding scheme managements for a feeder, a connected domain and the whole distribution grid. The other approach is based on Tabu search algorithm. The set of tripped switches is used as candidate solution. Some virtual tripped nodes are defined at the end of terminal nodes and beside the source nodes. The neighborhood searching is committed by moving a tripped switch to the adjacent node of its upper stream or down stream. The electrical limitations, the allowed voltage range and the required topology are used as the constrains. The former has the advantages of less calculation amount while the latter is able to handle more complex indexes and constraints.A heuristic methodology of expanding plan is proposed. The possible expanding schemes are listed according to the critical, weak and bottle-neck parts found out from the anti-fault evaluation of the distribution system. A heuristic principle is adopted to minimize the entire load shedding with the constraint of the allowed investment.The way to manage safe switching steps of network reconfiguration is suggested. The switches to be operated are categorized into two classes, based on which, an approach to form the switching operation sequence for both restoration process and return-to normal process is suggested. The loads with larger lost costs are restored in a higher superiority. The overload of feeders and loop in topology are avoided in the processes, as well.In addition, improvements are made on the existing simplified model of distribution grids. A new kind of structure is added to describe buses. The loads are described as random variables of normal distribution. The requirements of anti-fault evaluation of the distribution grids with certain or uncertain loads are met with the improved model.Based on the proposed approach, a set of fast restoration system to avoid a large area breakdown of distribution system has been developed and applied into practical uses of a utility. It has played an important role in building and expanding the public and mining power distribution systems and avoiding the serious effects losses due to long time large area breakdowns.