Sensing Switchboard Arc Faults

Abstract

In the late 1970s, the Navy recognized that electrical fires were becoming a major problem in submarines. Approximately three fires per year were occurring in the main electrical distribution switchboards across the submarine fleet. These fires have a major impact on mission readiness and could potentially cause loss of life and ship. In three-quarters of a second, the current from the smallest shipboard generator can bum a fist-sized hole in the side of a switchboard. The damage initially increases exponentially with time, limited only by available current from the generators. The Johns Hopkins University Applied Physics Laboratory (JHU/APL) worked with the Navy to design two basic arc fault detection (AFD) and continuous thermal monitoring (CTM) systems. The first systems were designed using all military- specification (Mil-Spec) hardware. At that point in time, Mil-Spec hardware greatly increased system reliability but it drove up the system cost. The most recent systems were designed using commercial-off-the-shelf (COTS) assemblies and parts and are cost effective for commercial use. These systems have proven effective in 450 V ac, 4,160 V ac, and 700 V dc switchboards. The timing on the systems is adjustable to allow for optimum usage with air circuit breakers or sealed breakers. While the AFD/CTM systems have seen extensive use in military ships, they are equally suited for the protection of all types of critical switchboards. Commercial ships, power generation facilities, power distribution switchboards, hospitals, web hosting facilities, etc., could all benefit from the increase in power reliability offered by this type of technology. These systems can be included in the original design of the switchboard or installed in existing switchboards with equal ease. At this time, JHU/APL is interested in licensing these systems for commercial applications.