Inclusion of voltage sag cost to underground and overhead subtransmission network planning

This study proposes the inclusion of the voltage sag cost to the network planning cost function. For that, this paper introduces a technique to establish a voltage sag distribution function in high-voltage meshed networks, consisting of underground cables (UGC) and overhead lines (OHL), by performing the three-phase short-circuit and by accessing statistic data of the considered network. For this, three cases were tested: typical Nordic 25-bus subtransmission network composed of both overhead lines and underground cables; the same network entirely composed of overhead lines; and the same network fully comprised of underground cables. The purpose of the case studies is to examine the impact of reliability parameters of these two distinct types of feeders on voltage sag and outage costs and therefore on the economic assessment of the network. To validate the assessment, data, such as repair time and failure rate, of the most important equipment from published Nordic databases are incorporated to this method as well as the comparison with the herein developed technique with unanimously accepted analytical methods. This work was performed considering the 110-kV subtransmission, the 20-kV and 0.4-kV distribution networks and constant load growth and interest rate for a project period of 40 years.