A Tutorial on Optical Ground Wire Ratings Analysis for Protection Engineers

Installation of an Optical Ground Wire (OPGW) is an increasingly common upgrade when replacing shield wire(s) on a transmission line, as it provides the added benefit of broadband communications capability. Utilizing such fiber installed inside the shield conductor comes with a substantial risk of damaging the communications circuit from annealing of the shield conductor due to ground fault current flow. The transient current-induced temperature rise on an OPGW is a simple calculation in itself, but sizing of an OPGW for adequate thermal capability requires careful consideration of numerous and often overlooked factors characterizing the total heating energy, many of which fall on the protection engineer to calculate. This paper provides a detailed overview of the principles and process to determine the required thermal withstand capacity of an OPGW and discusses a particularly complex case study with a novel mitigation solution.