A Cost optimization methodology for design of substation earthing system

Abstract

Current practice for earthing grid design for AC substations is mainly guided by IEEE 80 ; 2000 standard. This practice is an iterative process of changing design variables until safety requirments for step and touch voltages and maximum earth grid resistance are met. During this iterative process, the assignment of values for design variables is mainly based on the experience and assumptions of designers. However, this practice is not guided by concerns about cost minimization. Since the earth grid construction occupies a large part of the total cost of AC substation construction, an appropriate cost optimization methodology for the earth grid design for AC substations should be fully identified. The aim of this work is to develop a cost optimization methodology based on a Genetic Algorithm using Microsoft Excell based on IEEE guidelines. This paper analyzes the effect of each earth grid design parameter on the total cost of constructing earth grid and formulation of the optimization problem. This work is also supported by a few sample calculations for a few real-time applications. The calculations show that the developed methodology ensures cost savings of between 30% and 40%.