Unsymmetrical short-circuit fault analysis for low voltage distribution networks

Protective devices in distribution systems are utilized to optimize the network reliability and to avoid or minimize the damaging in the circuits and the instruments. The considered method and the level of the protection, is under various factors. One of the most important tools in selecting the type of the distributed system's equipment is evaluation of the short-circuit current correctly. In addition, this analysis is very noticeable in allocation and setting the protective devices in any networks. In this study, a novel method is presented in order to analysis the unsymmetrical fault occurs in the low voltage distributed networks. Initially, regarded to a complete model, the line impedances such as overhead and underground line impedances, in the network are computed and the methodology and modeling associated with two relationship matrices BIBC and BCBV is described. Then, the calculations method for the fault's current is evaluated by defining a new model consists of four matrices. Therefore, a program is provided for determination of short-circuit current, identifying the branches which carry short-circuit current and the results of it on the voltage profile, according to presented equations and Delphi software. At the end, all connection types and their results on the network are evaluated on a real low voltage network. © Maxwell Scientific Organization, 2011.