Inrush current requirements analysis for FAA facility power systems

Martin Marietta Corporation was tasked to perform an analysis of developing a new inrush current requirement which will be cost-effective and technically acceptable for facility power system stability and which can be met by adequately designed electrical/electronic equipment. This analysis of an allowable inrush current is based on the characteristics of the facility branch circuit breakers which provide power to subsystems on the critical bus. A recommendation is made and an inrush current requirements curve is developed to replace the existing limits stated in FAA Order 6950.2c and FAA G 2100e. The curve identifies a range of inrush limits to be imposed by comparing the amount of inrush a system is allowed to produce versus the length of time a system should be required to return to within 110% of the normal steady-state condition. Requirements developed from the curve are based on individual system measurements (shorter duration requirements) as well as facility circuit breaker characteristics (longer duration requirements). Systems falling between these limits may not exceed the requirement identified at the curve. As a result, a significant FAA cost avoidance can be realized when special soft-start devices are not needed for all equipment, thus allowing greater use of commercial-off-the-shelf equipment.<>