Cause of Arcing Inside a Medium-Voltage Arc-Resistant Metal-Clad Switchgear Compartment on a Sunny Day Without Any Evidence of Switching Surge: Recommendations for avoiding future incidents

Abstract

This article describes the cause of an arc fault in the cable compartment of a medium-voltage arc-resistant metal-clad switchgear (MV ARMCS) integrated inside an outdoor enclosure. The manufacturer of the outdoor enclosure for the switchgear was not the manufacturer of the arc-resistant switchgear. The arc fault occurred when there was no operator inside the switchgear to initiate the fault. The arc fault on a sunny day occurred without any evidence of a power system switching surge and without maintenance personnel touching the switchgear. The issue of missing hinged flaps is discussed in this article. An analysis of fault recordings captured by the digital protection package establishes that the arcing fault generated arc fumes with pressure that were exhausted automatically by the arc exhaust chamber assembly out of the switchgear through a wall-mounted louver. After the arc fault incident, the maintenance crew along with technical staff noted that cable insulation damage occurred due to outside moist corrosive air entering the cable compartment. Every time the wall-mounted louver opened and closed with a wind draft, air would become trapped and reach the cable compartment. Without a hinged flap at the top of the cable compartment, moist corrosive air degraded the cable insulation, causing the arc. This article provides recommendations and conclusions to avoid such incidents in the future in arc-resistant switchgears.