A Protection Coordination Index for Evaluating Distributed Generation Impacts on Protection for Meshed Distribution Systems Using Hybrid GA-NLP Approach

Abstract

The current distribution system can accommodate a limited number of distributed generation(DG) due to voltage profile and short circuit variations which consequently affect the power quality and protective relaying and the situation becomes sever with the increase in the DG penetration level. The amount of DG penetration can be limited by the conductor ampacity, voltage regulation and short circuit currents.

A new approach is proposed to determine the "protection coordination index” (PCI), which can serve as an effective measure when planning the protection of the meshed distribution system with DG. In this paper a hybrid genetic algorithm (GA) – nonlinear programming (NLP) is proposed to determine the PCI. The initial value of time dial setting (TDS) pickup current (Ip) of the relay is determined using GA technique and finding the final value using NLP method. The PCI is determined by optimally calculating the variations in the maximum DG penetration level with changes in the protection coordination time interval. This study is done on the distribution section of IEEE-14 bus system and analysis on how the capacity, type and location of DG can have an impact on protection coordination of directional over-current relay for meshed distribution system is determined.