Coordination Studies & Arc Flash
Additional Information
The Coordination Study determines the proper selection and short circuit ratings of protective devices. It includes protective settings to prevent damage to cables and electrical equipment, and setting adjustments to isolate and interrupt fault currents while maintaining service continuity for unaffected portions of the system. The design application and selection of breakers can be verified to satisfy the mutually contradictory objectives and requirements for selectivity and system protection.
There are three major aspects to consider when performing a protective device coordination study: safety, equipment protection, and protective device selectivity. Safety requirements are satisfied if the protective devices are rated to carry and interrupt maximum load currents and withstand and interrupt maximum fault currents. Protection goals are fulfilled if protective devices are set to operate above normal load conditions and below equipment damage curves. Selectivity objectives are satisfied if during a system fault or overload condition, a minimal amount of electrical equipment is removed from the system. The purpose of a protective device coordination study is:
• To specify the proper protective devices (relays, fuses, and circuit breakers) to protect distribution equipment,
• To calculate the proper circuit breaker trip unit and protective relay settings to minimize damage to the faulted component and selectively remove the faulted device from the power system,
• To ensure that protective devices do not operate under normal load conditions,
• To generate the time-current curves (TCCs) needed to perform an arc-flash hazard study on the power system.
Arc-Flash Hazard
Additional Information
An arcing fault is the flow of current through the air between phase conductors, or phase conductors and neutral or ground. An arcing fault can release tremendous amounts of concentrated radiant energy in a small fraction of a second resulting in extremely high temperatures, a significant pressure blast, shrapnel hurling at high velocities (in excess of 700 mph), and severe or fatal injuries to personnel. The purpose of an arc-flash hazard study is:
• To specify the protective clothing and personal protective equipment (PPE) required for the application,
• To determine and label the maximum incident energy available at every location along the distribution network likely to require examination, adjustment, service, or maintenance,
• To determine the arc-flash boundary distance (safe working distance) that must be maintained by unprotected plant personnel.
The Incident energy and arc flash boundaries are calculated following the NFPA 70E and IEEE 1584 standards.
OSHA enforces safety-related practices in the workplace. Employers are required to provide a workplace assessment to determine if hazards are present, and must select the proper personal protective equipment (PPE) for personnel working on or near energized equipment. This requirement is intended to reduce the occurrence of serious injury or death due to arcing faults.
Custom Labels that display the Incident energy are available through a complete arc flash hazard study performed. These labels are generated based upon the results of the short-circuit study.
