Sectionalizing / Arc-Flash Studies

Sectionalizing: Proper sectionalizing of a distribution system can have a considerable effect on continuity of service and overall system reliability. Strategic placement and coordination of protective devices (breakers, fuses, sectionalizers, etc.) can limit fault-induced service interruptions to the fewest possible customers and the shortest possible time. Proper sectionalizing will protect the distribution circuit and associated equipment by providing desired responses to different types of faults.

A distribution system that has proper sectionalizing has the following characteristics:

• Service interruptions are minimized in terms of frequency and duration
• System distinguishes between load current and fault conditions
• System distinguishes between temporary and permanent faults
• Fewest number of consumers affected during fault conditions
• Sectionalize longer, lightly loaded line sections to protect up-line consumers

Arc-Flash: An arc-flash assessment is performed to determine the level of threat the electric system presents to utility workers, property and the general public in the event of an unplanned arc-flash (or, flashover) of a system component or components. The assessment identifies risk level s using a system of metrics which differentiates high, low and average risk locations across the service area. Arc-flash assessment and mitigation planning are now mandated by all major national safety codes, including NEC, NESC and OSHA, as well as State and local codes and standards. Since an accurate model of the electric system (including properly-modeled sectionalizing and fault-clearing devices) is important for a successful arc-flash study, the arc-flash study is a natural extension to a sectionalizing study and can be merged into one efficient and cost-effective study activity. An Arc-Flash Assessment is typically:

• System-wide in scope
• Provide useful information for supporting appropriate operating procedures and safety program
• Identifies “strategic locations” in order to minimize calculations
• Limits variables by using prudent assumptions
• Focuses on key results - Arc-Flash energy level and safe working distance

Benefits of an Arc-Flash Assessment include:

• Provides a “visual database” for the arc-flash conditions and parameters around your service area
• Provides insight into where potential arc-flash “hot spots” exist (and where they do not)
• Satisfies the requirements of NESC 410A3 and related regulations
• Quantifies arc-flash components throughout system
• Limits risk and reduces exposure to loss by aligning threat levels with operating procedures and personnel protective equipment