Saving Lives Six Feet Under With Light-Based Arc-Flash Protection

The topology and protection of underground power systems in urban areas are very different from overhead distribution systems. Since the inception of these systems, network protectors and fuses have been used as the main forms of protection and isolation. Unfortunately, these devices do not provide the fastest isolation for arc-flash events that occur in underground systems. This lack of speed can put the safety of personnel working inside an underground vault, as well as the public above, at risk. Light-based arc-flash protection is a modern technology that has been used to successfully protect personnel from arc-flash events in industrial switchgear for years. This paper explains how a large utility in Texas modernized their underground protection schemes by adding light-based arc-flash protection to detect arc-flash events in the vaults. They also added an interrupting device to their vaults to provide faster and more selective isolation for transformer faults. These two improvements increased the speed of protection and improved personnel safety.